I believe niche is First Watt, with Pass Labs intending to have mass market appeal.
On the original topic, I just brought in a loaner/demo XA30.8. It still needs to break in according to Reno Hifi, and should be ready for real critical listening by Sunday. Early impression: I would agree that the XA30.8 could be characterized as having somewhat tubby bass. But it's going to depend on your reference. It's better in terms of being tighter than .5 series bass, and it's certainly not stereotypical farty tube amp bass.
As far as low power vs high power, there are going to be two camps. The XA30.8 is said to appeal more to SET crowds as a result of its big tone, but then as you go up in power, the bass control (and other technicalities) are said to improve. Many folks prefer the overall sound of the lower power models for their preferences and vice versa.
Time will tell if I keep the XA30.8. I should have some good listening time this weekend.