DSP Limit Question

Not a UAD user but if you only have a compressor on the buss rather than on each track then this would reduce your UAD DSP usage.  Thereby freeing up UAD DSP processing for other plugs.

If you need a comp on each track could you not use the Pro Channel?

if each track has different compression setting (every compressor is set different) and you need to have a compressor on each track...
 
Freeze it.
 
freezing the track puts it in a deep sleep state. where you cant do a lot of changes to the clip unless you unfreeze it.
but freezing a clip sounds exactly like the original with no change at all.
if you need to make a change to the compressor settings, simply unfreeze it. then freeze it again.
 
IMO, using a compressor on a bus is good for parallel compression and some effects but if you need it to reduce gain it will only work if every track is of similar origin (all guitars / all drums)
and even then it produces a sometimes unwanted effect.
 
Set attack and release times never sound good across the board / on all instruments unless your putting it on your master bus in the mix down stages. (IE-Waves SSL G) using it sparingly for Pre Master.
 
Wookie had a good idea though, Use the PC compression if your UAD is chewing up CPU.