Why buy a UFX just for mic pres?  Seems like a dedicated multi-channel pre with ADAT outputs would be better value (unless you need a second sound card for some reason). 

Yes you can connect the two via ADAT.

I don't have any external mic pre's now, just the 2 in the UCX.  It's likely that the 4 in the UFX will hold me over for quite a while so I bought that to replace the UCX as my primary interface.  I just figured since I've got both in the rack I might as well have 6 pre's instead of 4.

The UCX has 4 analog line inputs. The Idea to use external pre-amp with 4 channels is good. But by that the UCX is full.

I would eventually still go for an UFX as this is still the flagship interface of RME. With that you have more options in terms of features and to connect external devices.

Then you can connect the UCX Pres and analog channels to the UFX via ADAT and control all via UFX inside DAW.
Another advantage, you have then 2 recording interfaces: one can act as a backup if one is either mobile or needs maintenance. Or alternatively you sell UCX and buy other preamp later if you think you require this.

The differences of UFX vs UCX you can look-up in this table:
http://www.tonstudio-forum.de/index.php … 16-01-pdf/

On top of the UCX the UFX offers:
- better design of preamps (parallel conversion)
- Direct USB Recording (DuREC)
- dampening of power-on noise on all outputs (only with UFX and 802), good if you have more than 2 monitors
- amount of I/O channels (60)
- fully stantalone capability, color display
- 2 x Midi
- 2 x Headphone Outs

With the exception of the parallel conversion (which is at best a very subtle improvement on just those channels that have RME preamps), all of the other features you list may be meaningless depending on what Joe (or any user) needs.  For many people, one headphone out and 6-8 channels of inputs may be plenty, and DUREC and a front display may be useless.  So I'd be wary of thinking UFX is always better than UCX - each is a different tool for different user needs.  Based on what little I know from Joe's post, I still think he'd have far better bang for the buck to invest $2,000 on some nice pres.

For the record, I own both - a UFX for my location rig (4 built in, clean pres are very handy, and the DUREC is essential for backup if my DAW fails) and a UCX for my studio (where it more than meets my studio needs).

Ramses - I don't intend to get into a back and forth on this.  My only point, which I believe I stated pretty clearly, is that each unit has different features and *depending on one's needs* some may be valuable, others less so (or even meaningless).  The UCX is not a lesser interface, just a different one.

Good luck Joe with whatever you decide.

Sometimes a technical discussion is good and needed. I personally supported the idea of the customer to go for an UFX and told my reasons.
This thread simply became stuck, as there was no response anymore from the originator of this thread.
A simple "and what about my other questions" would have been enough to reactivate it.

To your question (when I write UFX+, it could be any primary device like UFX, UFX II, ...)

Generally to what device to choose best as master:
Best take the device as master which has the most number of channels and connect it directly to the PC.
If you change then the sample rate i.e. in your DAW, then the master and all slaves will get the correct clock automatically.

Cabling between recording interface and computer
As both devices need to be operated by TM FX, you need to connect UFX+ and UCX to the computer with the type of digital interface as you like (USB, thunderbolt, Firewire).
So you need to install the required drivers for UFX+ and UCX.
Note, there are 4 separate drivers, 2 for the UFX+ (USB/Thunderbolt), 2 for the UCX (USB/Firewire).

Digital cabling between interfaces UFX+/UCX
-From the master you need at least one digital output towards a slave so that it can receive clock. So you need i.e. ADAT in 2 directions between UFX+ and UCX a) to get the additional channels via ADAT (IN) b) to send clock to the slave device and eventually use any of its outputs
-Connect UFX+ as primary interface.
-Connect UCX to UFX+ via ADAT (both ways).

In the RME driver settings dialog:
-UFX+: set clock to internal (master)
-UCX: set clock to be received from ADAT.
The ASIO buffersize needs to be equal on both devices !

In TM FX:
-You can open a 2nd instance of TM FX. One to operate the UFX, one to operate the UCX.
-Any to Any routing works only inside of each TM FX instance. But now you can start to route any of the UCX inputs to the 8 ADAT outputs, to get i.e. the 2 additional Mic inputs and 6 further analog inputs added to the UFX.

In your case
There should be no doubt about it to connect the UFX+, which has more channels, directly to the PC.
Then the UFX+ will be set by you to master.
The UCX becomes slave.

Which connection to the PC (UFX+)
- Whether you choose thunderbolt or USB3 doesn't matter much in terms of RTT times, maybe thunderbolt has a little advantage in terms of CPU load, but tbh, I didnt see a big difference in terms of CPU load even between i.e. USB and Fw, as the RME USB driver are really good
- The thunderbolt driver is the only one which supports the pitch function of the driver, in case you need it
- It can have more advantages to use the MADIface driver (USB3/2) because then you have also access to additional recording interfaces or converters by this one driver as the MADIface driver supports a number of different devices. By this you can have direct access to each of the devices from DAW with this one ASIO driver. You only need to be careful in 2 aspects: the devices need to be clock synched and you need to set on all the same ASIO buffersize.

Optimizing / reducing cabling to PC
You could use the UCX standalone capabilities to eventually remove the USB or Firewire cable once your required routing (2 Mics and 6 analog INs through ADAT) has been set and stored to 1 of the 6 user profiles in the UCX.
But I am not 100% sure, whether you can set/change Mic gain or autoset on the device in standalone mode.
So this might be a reason to keep the USB or Fw connection of the UCX to the PC.

If there is any further question on your side, then please ask.