If you are interested in the Empress I would also encourage you to investigate the Keeley Compressor Pro for these reasons:
1. It is in the transparent compressor camp like the Empress
2. Incorporates gain reduction metering like the Empress
3. Is highly configurable like the Empress
4. Depending on what settings you are intersted in the Keeley can be more flexible than the Empress. I.E. control of ratio and hard vs. soft knee which can make a big difference in how the compressor "feels". That being said, the three ratio settings on the Empress will probably be enough for almost anybody but you can fine tune with the Keeley's knob.
5. The Keeley can also be used as a limiter more effectively than the Empress.
But the perk of the Keeley that impresses is the Auto Mode which is great for those times when either you switch between basses or are having a hard time dialing in. Auto Mode almost always just plain works and sounds great.
While it is almost identical in size to the Empress, the Keeley has top mounted jacks which may be helpful for your pedalboard setup too.
Not trying to throw a wrinkle in your decision process but I'd be remiss not to mention it for consideration.
Here's my review of the Keeley Compressor Pro:
Testing Compressors: Cali, Smoothie, Empress, Diamond, Keeley, FEA, Darkglass, Doc Lloyd, JHS & more