I have an Eden WT-550 and it is very similar to the 400. It's really important to get the gain structure set right, as the amp comes alive when it is.
With passive Fender basses and flat EQ (no enhance, I always run it flat) I am usually between 2:00 and 3:00 on the gain knob. I have plugged basses in that needed up to 3:00 but not 4:00. But I don't play with a light touch, either, so YMMV.
I wouldn't worry about where the knob is if it sounds good, but you might want to check the line on the knob lines up with zero when rolled off all the way. The little red face on the knobs can move sometimes.
Re: compression, the 400 like the 550 has a very rudimentary compression feature that really acts more like a limiter (don't ask me for technical details, I've gleaned this from the Eden Forum). I do know from experience it doesn't offer much in the way of true compression and it isn't really adjustable. I leave it on, though some hate it and use an outboard compressor if they want the real effect.
I agree Ashdown has a thick quality compared to Eden, I compare it to Ampeg tone somewhat, at least in that tradition. But I would seriously recommend you keep the WT400 long enough to try a few different cabs with it before going to an Ashdown combo. You will probably find an amazing rig and will have more flexibility. I find in general Eden heads match up well with most cabs.