Mine is in my sig.

I'm sooo close to buy a Fireface UFX. Very interested to see if you can get it  to work Soundsubs.

On both my systems I use the ufx with I have not seen this issue on either firewire or USB. Currently I'm running the ufx on my i7 laptop using the USB connection.

Well looky here:

http://www.rme-audio.de/download/fut_usb_win.zip

New firmware out yesterday.

wow, after that 353 firmware update, I no longer get the pop/clicking on start/stop. Now to go and see if it fixed my performance issues.

Glad at least part of it is working better, and hope the other parts are too.
 
Firmware is a wild one - I cannot tell you the last time I even looked for any firmware updates for something.
 
Good news indeed, 
 
Bob Bone
 

The new firmware may have helped reduce the lag when I click the record arm button, or it may be wishful thinking.  Performance overall seems better.  The issue with changing sample rates is the same, and I still get some pops and clicks when exporting or making edits to prefences. 

I am using the UFX in X3 Via firewire and have not seen these issues. I know its pretty basic and you are probably already aware, but those of you having FW issues make sure you are using a Texas Instruments FW chipset.

The lag on the record arm button is a classic interface problem. When I originally got my Focusrite Saffire I had exactly the same issue until Focusrite got rid of the bug from their drivers. So this is definitely without a shadow of a doubt drivers or firmware in my mind (the two go hand in hand). Well that's what I think... Cheers..
 
 
(EDITED: Last line I wrote didn't make sense) 

Further thoughts...
 
If you haven't already please try disabling Allow Arm changes During playback/record.
in Edit > Preferences > Project -> Record (this worked for me whilst I waited for Focusrite to fix my issue)
 
And also try experimenting with disabling or enabling with Always Stream Audio though FX in Edit > Preferences > Audio -> Playback and recording.
 
Ta