Actually, the bass sounds terrific through the Epi rig...just as my last MB-2 did. I had an indoor casual on Tuesday night, and I used it for the first set through the 502/310-2. The volume was fairly low, but there were no issues with controlling the sound. As you'd expect, it's certainly deeper than with the GB rig, which is very mid-happy, but overall it still sounded like a Rob Allen.

To compensate - which is really too strong of a word in this case - I played a wee bit closer to the bridge. I'll be running through the same rig on an outdoor casual this evening. Assuming the ambient noise isn't overbearing, I'll share some sound clips to gauge everyone's thoughts.
What I love about my Epi rig (and I know this is a tangent...apologies, but I think it's worthwhile since Ken mentioned the tone he hears from my MTD clips) is that, while it certainly has its own characteristics, to my ears it very accurately represents the sound of each instrument. In other words, the MTD's sound different than the Roscoes, which are likewise unique from the Sadowsky, Lakland, and certainly the Rob Allen. I will EQ to the room - which can occasionally be a struggle - but there's very little, if anything, I have to do to capture the sound I'm after from each instrument.
The bottom line for me... my absolute favorite thing about the Rob Allen is that the sound is completely in your hands. Vary your hand position and touch, and the array of sonic options is amazing.