Please provide URLs to the both mentioned products and what problem you have that you want to get fixed by those.

Also detail, what type of connection you have between PC and ADI-2 FS, USB, optical or coaxial SPDIF ?
The ADI-2 FS is no USB DAC / has no USB port, so any product claiming to pimp-up USB is of no use.

Or did you mix the RME products ? Besides the ADI-2 FS (without USB) there are also these two different products which are - among other things - USB DACs: ADI-2 DAC FS, ADI-2 Pro FS (R BE).

Regarding galvanic isolation: if you have no hum or do not hear hum, then you do not need galcanic isolation.
Never had such issues using USB, do you have any issues ?
Otherwise use optical SPDIF, where possible.
Tip: do not try to solve problems, that you do not have using devices where you do not exactly know how they work and could most likely even introduce problems or simply suck money out of your pockets but being completely useless in your setup.

Regarding jitter elimination: see the following video about Steadyclock FS. This is RME technology which already eliminates any Jitter from digital inputs very successful.
EN: https://www.youtube.com/watch?v=Ti0aHW-zYcs
DE: https://www.youtube.com/watch?v=6rcBVuWOHiw

If you would have ADI-2 DAC / Pro then you could already check and come to two very valuable conclusions:
a) CRC check in the driver .. validation to not have any USB transport / cable problem
b) the so called Bit test to validate lossless audio transfer end-to-end in the digital domain between audio player and ADI-2 DAC/Pro up to the DSP shortly before the D/A conversion which happens without any jitter (Steadyclock) and with the internal FS clock of ADI-2 DAC/Pro in highest quality.

Sorry for that, casue my first time to post and quoted, and make typing mistakes
I m using PC --> usb cable(AudioQuest Coffee USB) --> adi-2 dac fs --> xlr cable(Inakustik 1204 air) --> active speakers(Elac Air-X 403),
saw from other forum using usb isolation product such as uptone iso regen make sound stage wider,
see if using such product will make improvement, thanks for quick reply

Sorry, but "Oh dear"
- AudioQuest Coffee USB - €300 (0,75m) - €800 (5m)
- xlr cable(Inakustik 1204 air) - ~€300 - >€1000 ...

You don't need all that, it's overpriced and not required.
The additional money you should better have saved or spend for room optimization or even getting better active monitors.

Regarding galvanic isolation and jitter reduction and all this stuff .. you got already an answer. Nothing more required.

If you do not hear any hum, then you have no issues with hum and need no galvanic isolation, save the money ...

In terms of USB cable you can validate this on your own using the Bit test, see ADI-2 DAC FS manual.
Even the least expensive USB cable will do as long as the plugs are ok and contacts well soldered.

In terms of XLR/analog cables you would need to perform blind tests to realize that there is not difference in cables.

Sorry, we had such discussions quite often already. In short: HiFi industry is not honest to you and only wants to earn money by designing nice shiney products looking better compared to standard cables, combined with a clever marketing / advertisement strategy. And this works well, because our brain/ear is not so 100% precise as you think, so called psychoacoustic effects seem to confirm this for the buyer. Why everybody is "so sure" that it sounds better.

Added to this is the fact that the users then fire each other up in forums, so that everyone thinks that there is something to it. And if, due to psychoacoustic effects, you yourself think you have heard it, then from the subjective point of view it is tantamount to a truth, but it isn't and you could find out if you used the right methodology in listening tests.

Therefore please google for "psychoacoustic" and why blind and double blind testing is required. You can also search the forum for the term "psychoacoustic". In a led blind or double blind test you couldn't identify sound differences.

I have a high end HiFi and am through will all this. Had cables here for test up to ~€1200. No audible difference.
ADI-2 Pro FS R BE - Accuphase E-600 - B&W 803D3 .. no "vodoo cables" .. on the speakers simply copper cable.
If you need longer speaker cables simply take copper 4mm² and that's it, really not more is required.

In contrast to that working on things like room acoustic or getting better active monitors or amp/speaker combination results in audible better sound.

Addition: I'm sorry if you should feel embarrassed in any way. But there's quite a difference between HiFi forums and a forum dedicated to studio gear, where your music is produced. Here you have the appropriate background or sound engineer training and you know all these shortcomings that we all have (psychoacoustics) and that you have to eliminate such factors for fair / objective  comparisons.

As I said, in the case of the transport of digital audio data via USB, it is even clear with a bit of technical understanding (and questioning back on RME forum, if something should be unclear) that such high expenditures for USB cables are completely unreasonable. If the sleeved cables looks better and you are happy to pay the price for it, then of course that is something else. But that doesn't make it sound any better.

One final remark: if your cable and add-on stuff is nearly as expensive as your HiFi devices then there is something very wrong by "design", kind of misconception from ground up.

To sum up

I wouldn't see this now not too negative, more like perhaps "lessons learned", at least you have good (looking) cables.

To your basic questions, the devices mentioned above are not needed for your ADI-2 DAC FS.

You have a phantastic DAC performing jitter elimination (Steadyclock FS) and where you can check for USB transport errors and perform a Bittest in the digital domain to ensure lossless transfer of digitized data. This is a unique feature of this device, this gives you a control that you wouldn't have with any other device. So you really have a solid basement.

Getting better sound ?

If you think sound / soundstage would require optimizations, then I would like to motivate you to experiment with different placements of the speaker in the room and to use tools where you can validate whether you get too many reflections or addition or deletion of frequencies which should be avoided.

Maybe you also need some correction of the room. And some things can be optimized with PEQ of your ADI-2 DAC.
If this is still not good enough, then sorry, in this case you simply need better speakers.

There are free measurement tools
- for PC (REW, room eq wizard) https://www.roomeqwizard.com/
- for iPhone the app "Audiotools" by Andrew Smith where basic functions are free of charge, recommended by KaiS e.g. in this thread https://forum.rme-audio.de/viewtopic.ph … 41#p178841

Thanks for ramses & Curt962 advice

Set D/A filter to "slow" and it gets more musical sound, as I never use the D/A filter before, Many thanks for your kindness reply!