Yay, the site is back and active!!
In the time the site's been down for me I've ordered and received my Ultra VI, and still have my Hellcat VI. It was a bit of an adventure; I placed my order on 22 May, and didn't get the bass until 7 July. Bit of an annoyance, but, it DID arrive
So, I've had the Ultra VI for about a week and a half, and I don't find it dramatically different than the Hellcat, sound wise, though they are different. I'd readily use either in a live situation and no one would likely hear the difference, really.
.: Solid playing bass, neck is thinner in profile than the Hellcat, and the set neck keeps it thin all the way up; no big heel like on the Hellcat
.: Light weight; it's gotta be a couple pounds lighter than the Hellcat
.: 3-way switches are too stiff; they work ok, but are much harder to flick than the switches on, say, my Jaguar. This causes you to too easily jump from one mode to the other, when you intend to turn a pickup off. uickly changing pickup selection while playing is difficult.
.: Output is relatively low. Despite the humbuckers, there's not a lot of power from the pickups. They sound ok, a little dark, but ok...
.: the design is not upgrade friendly, at least for pickups. The mini humbuckers are an odd size to swap out, and being body mounted will require body fill or routing to use singles or full size humbuckers. Adding switches to the pickguard shouldn't pose any issues if you want to alter the circuit itself.
Yesterday was really the first time I've been able to play the Ultra through an amp
It passed the test well enough. Used it for a 3hr practice session, then played two gigs through the day with it. Sounded good and played well through it all. No issues with getting lost in the mix or what have you; it sat nicely in the bass role and where I use it as a baritone, it cut through just fine.
Something I did find, however, that differentiates the playing experience from the Hellcat is in basic ergonomics while standing. The body shape of the Ultra results in the neck seeming longer than on the Hellcat, where the contours bring the bridge/nut further towards your picking hand. This makes forming, say, and F barre chord a little more difficult. Sitting, they're pretty similar, but standing it's a little harder to reach all the way down the neck... feels more like playing a full scale Jazz Bass, for example.
I did a bunch of recordings of both instruments covering several pickup selections, keeping everything else equal, even putting a fresh set of LaBella HC-6Ns on each first and making sure to keep my picking location constant.