BBF Pro and BBF Pro FS are the same plus enhancements that are clearly described on the webpage:
https://www.rme-audio.de/de_babyface-pro-fs.html

- +19 / +4 dBu switch on the bottom adds a direct way to reduce the output level, thus improves SNR for sensitive active monitors, avoids distortion / overload, and helps to keep TotalMix FX faders near 0 dB instead of high attenuations.

- Full SteadyClock FS circuit as in the ADI-2 Pro FS for lowest jitter and highest jitter immunity.

- 3.5 mm TRS phones output power rises from 70 mW to 90 mW. THD of both phones outputs improved by up to 10 dB. Uses same output op-amps as ADI-2 Pro now. Output impedance of 3.5 mm TRS lowered from 2 Ohms to 0.1 Ohms.

-   Mic inputs SNR improved from 112.2 dB to 113.7 dB, TRS Line inputs SNR improved from 114 dB to 116.3 dB (120 dBA). THD Line inputs improved by 8 dB.

- 6 samples less latency on the AD side by new ADC (5 samples AD, 7 samples DA. It won't get quicker...).

- All the above improvements were achieved without raising the units power consumption.

- K-slot for theft protection.

Question: is there something difficult to understand? What is unclear?

The difference of technical data (phones output, etc) you can also see by comparing the manuals (technical section with all technical data) or by using my Excel:

In this blog article I provide an Excel where you can compare the different recording interfaces for USB/Firewire/TB:
The blog article: https://www.tonstudio-forum.de/blog/Ent … B-MADIfac/
The direct link to the Excel: https://www.tonstudio-forum.de/attachme … 4-08-xlsx/

I'm really very sorry, I can't see in the link you gave any reference to the enhancement effects I referred to.
I don't think you and me are referring to the same "effects".
You probably meant to Total Mix effects.

I'm referring to non professional effects, those which placed in Windows control panel, in the well known "Enhancement Tab".
Those effects are not for production or anything professional, but for someone like me it does enhance the experience of listening to music as a pure audiophile in many levels. Having or not having these effects are a deal or a deal breaker for me.
I think it is reasonable that some customers going to use this card not only for production and "pro usage" but also for audiophile, home entertainment and even gaming. Especially given that the Babyface line is mainly for home studios\amateur musicians and not for big professional studios.

To tell you the true, I'm pretty sure that if Babyface Pro has those effects, then the Pro FS also has them. but I must confirm this before making a deal.
I'm attaching a picture of the effects interface I'm talking about:

I'm back to you now with this issue because I need to get a new interface soon for a second desktop station.

Thank you MC.
I know these enhancement are driver dependent, but unfortunately most manufactures don't bother to incorporate these features in their drivers, and I must give a high five to RME for implying this in their drivers. As I said, these audio effects do a night and day difference in my audiophilic experience.

Now about the integrated headphone amp, lately I use a low impedance in ear headphones, with 18 ohm impedance.
I'm not a fan of open back headphones and aside from what I use lately, I also a fan of headphones like Audio Technica ATH M50X, and Sennheiser HD280 Pro. Those are not high impedance headphones. Just giving you a picture of my general direction with headphones.
So given my preferences, do you estimate that I'm going to feel an improvement with the Babyface Pro FS?
I feel that the headphone amp in the Babyface Pro is almost not strong enough. It does the job, but barely. Because you know how it is, an amp usually doesn't sound great when it is on 80% or above of it's power. It would be optimal if everything will sound loud enough in 50-60% of its output power. Of course it is depend on the recording\music file, and I feel this lacking mainly in recordings that lack in volume.
That is the only weakness I've found in the Babyface Pro.

All these can be easily used with the BF Pro.

And I feel you are on the wrong path. If the music...

...is too low in volume then you don't need more power, but more level. Use TM FX, you can easily add 6 dB on the playback side and up to 6 dB on the phones output channel.