The True Sub Mark IV is the current version of the Mark II. Sorry I'm a little out of date. In my opinion, the Architectural Signature might be a little more than you need, unless you're really into big bass. If you get it, you should certainly have the low end covered. Personally, I think its better placement flexibility (versus the driver/passive radiator regular version) can be a meaningful advantage depending on your room. If you later upgrade your main speakers, you might feel good about not having to upgrade your sub.
I have found that a good number of Audiogon posters prefer REL subwoofers, generally described as more tuneful -- better able to distinguish different bass frequencies. I once had a REL Strata II which was OK but didn't bowl me over. I am told that the quality steps are large between REL products, and the bigger ones are much better.
To me the Sunfires sound good, within the parameters I described above. I haven't really found them to be afflicted with rubbery, boomy resonances, as some others have complained. Perhaps room and placement are big factors here.
I like Bob Carver as a designer. As you may know, Bob has been controversial in high end circles for decades, beginning with his "Carver Challenge" in early Stereophile pages. I think he has gotten better over time. I regard the Sunfire subwoofers as cool products that are manifestations of at least two novel technological advances (in drivers and in amps), although copycats (or OEMs?) have appeared in recent years. For what it's worth, the Sunfires have received generally (if not unanimously) favorable reviews in the audio press. Good luck.
