Thus far - due to rehearsal space restrictions - the amps are quite close to each other. I hope to have a little more room at the gig tomorrow night.
However, the stereo effect is still apparent. Hard to describe, but it's just a bigger, more complex and more versatile sound. What appear to be minor tonal adjustments in mono mode are more apparent in stereo.
This is probably due in large part to clarity - the greater the headroom, the more apparent the tone adjustments. Since a separate amp is dedicated to each pickup, the bass pickup (normally the dominant one for me) does not have the opportunity to overwhelm the treble pickup (unless I want it to) - I can control the amount of its influence via both volume and presence (tone). And, the icing on the cake is the global master volume, which allows the bass to come up in the mix (or recede) quickly as needed - without changing pickup blend or tone.
As for too much gear - not an issue with these amps. The Amp One is a small cube app. 12" x 12" x 12" and the Amp Three is only slightly larger. They each weigh about 40 lbs and come with a padded carry bag with a pouch for cables, etc. If I had a padded gig bag for the bass (I know - blasphemy), I could sling it over my shoulders and pick up an amp in each hand and be off.
IMO, these AER amps are a really good match with Alembic basses in general, and particularly with the Series basses, for any application other than a really large room or outdoor venue.
But, they do have an XLR DI output and a 1/4" line out on the back and I'd be willing to try that through a PA for larger stages.
Unfortunately, they're not cheap, but neither are our basses, and you get what you pay for.