Firewire. Using external power. But since you ask, I'll try using only bus power.

Also, I downloaded and installed the latest firmware from your site. (Installation worked correctly as, per the instructions, I installed the USB drivers and connected that way.) Had downloaded and installed the latest driver, too, but rolled it back to the version that had shipped with the unit.

The USB settings, btw, will open no problem. It's the firewire settings and firewire mixer that are affected.

At worst the workaround is to just access the mixer each time I power on the UCX, but all things being equal I think the software should be accessible anytime the mixer is already running. In other words, I should be able to close the mixer program and then reopen it, provided the unit remains powered on.

In any case the sound quality is outstanding. Simply outstanding.

A couple other comments:

A lot of work went into producing a nice, spiral bound manual. That manual then should be written more clearly. Use a subheading, for example, titled "Routing" to explain how to route signals. Probably for you, and for longer time RME users, it's just obvious, but for others not so much. It's a real selling point to be able to say "It's easy to use and extremely powerful mixer software," but if people look at it and think "it's complicated and intimidating and I can't figure it out" they'll be less likely to buy a unit.

Speaking of packaging, the physical packaging -- the box the UCX came in-- was beautiful. Very well done on that score.

The unit itself is constructed to a high level of precision, with two exceptions. The power attachment point seems flimsy and ill-fitting. The jack fits into the socket, but only after a little bit of fidding, and it seems ready to fall out at any time. Similarly, the front XLR jacks seem to me a bit loose fitting. They manage a positive lock on an XLR cable but the cable still wiggles around quite a bit. I would try to make that a more snug fit.

Otherwise, once I've gotten used to the unit, I look forward very much to using it for my weekly podcast.

And, hopefully, drivers will be compatible with Mountain Lion!!

Am using firewire. Per instructions for firmware update I installed the USB driver and connected w/ USB for the firmware update. But that was only for the update. There is now no USB connection, only firewire.

Yes, my thoughts exactly.

To reiterate, and I've just done this a moment ago, after updating the drivers to the latest version from this website. Firmware, per above, also up to date. OK. UCX is powered down, connected only by firewire. No bus power evident from firewire. Power adapter plugged into unit. When I power on the unit two software icons appear as open programs on the right side of my dock: Fireface USB Settings and Totalmix. Clicking on Totalmix opens it up, seems to work normally. Clicking on Fireface USB Settings opens it up also, and it seems to work normally. With UCX still powered up I close both programs. When I click on Fireface USB Settings to open it up again, it does. But when I click on Fireface Settings (which is, if I understand correctly, the firewire settings connection) nothing happens and the program won't open. But now, when I click on Totalmix, it does open. On that, perhaps a firmware/driver combination? I thought, btw, that the new driver overwrites the old one, but evidently it leaves Fireface Mixer in place? Fireface Mixer still won't open, but that's not a problem if Totalmix is opening normally...

Not sure if this helps, but that's what's happening.

OK. Done. But what about the program "Firefox USB Settings" popping up when I turn the unit on? And will this program change the settings even when only connected by firewire?

Just to repeat to ensure clarity -- no USB cable is connected, only firewire.

Not a Hackintosh. A new -- purchased directly from Apple -- Mac Pro hex core. As stated above, boot drive is an OWC Mercury Accelsior PCI-e SSD, and that's where the app is installed.

The Fireface USB Settings that pops up is ver. 1.64 and Totalmix is ver. .0983. Firmware update is Fireface USB Update 2.74.

Well, as far as I know it's from fireface_x86.zip -- so where is this 1.73 driver located?!

All we say is:
- the Fireface Mixer will not work with the UCX (that is the old TotalMix for Fireface 400/800)
- with both FireWire and USB driver installed, using their latest versions, the wrong Settings error does not happen for us.

That brings me to fireface_x86.zip. That is indeed the FireWire driver package, but which version did you install? The latest on our website is 3.09. An older one might cause that trouble as well.

It could also be that the whole driver installation is a bit messed up now and you might be able to clear it by deinstalling the drivers manually as explained in the manual prior to reinstalling the latest versions. Even better: as you needed USB only for the firmware update you could remove the driver without reinstalling it.

FIXED. BUT...

OK, after deleting and reinstalling both USB and firewire I've now got it working.

But, here's an odd thing: Using firewire bus power only the polarity of the power switch is now reversed. "On" is "off" and "off" is "on." Maybe this has something to do with the software glitches?