I was the same way, but once you get it dialed in sat sub is amazing... A really nice bookshelf sounds better than a tower except on the low end IMO anyway, towers have larger cabinets {resonance} and I have yet to see the 6.5" woofer that can reproduce bass as good as a 12" subwoofer?... I have tried this out with my evo10 bookshelfs vs my evo40 towers with the same subs and crossovers they sound a little better, but I don't turn the subs on all the time so sometimes I just run the towers...
The most important part is the crossover, and doing it before the amp, but I have had good luck with f-mods, you can have them custom made and I tried a few different ones every time... I have had custom xlr ones made too... But the best way to do it is with an eq of some sort, I had an XSP1 and gave it to my brother because I thought it would tune better then my fmods but it sounded almost the same, and I prefer the simple dac to amp vs all that circuitry and confusion...
But I have played with the ULS15 dual drive {I have a single one} ascend sierra towers, xpa2 amp and xsp1 preamp, we ended up crossing the sierra towers around 70hz to the subs, but that xsp made it so easy, he also bought all emotiva XLR balanced cables and used them to connect the amp and subs, the xsp has dual sub outputs, it came really nice... But that system sounds amazing, I actually talked 3 local guys into this setup in some variation {on the subwoofer side}... For around $6000 the system is hands down the best I have heard, The parlor jeff has his setup in is 650 sq. feet with 18ft cathedral ceilings, and it fills that room with hardly any effort!!! I will upgrade someday, maybe in 5 years or so when my evos are getting old...
I would love to see how that system measures on one of your audio geek systems... I know the sound is fantastic....
Alex maybe this winter when I slow down you can take the 2 1/2 hour ride down, or maybe in the spring, we have a giant party, pools heated (although no one goes in), we have music (live and ipod), food, drinks, this year we had a 50ft water slide, rock climbing wall, and mechanical bull riding.... the party goes from 11am to 2am... This year we had around 200 people at once and probably 300 people total.... On a few occasions throughout the party, I threw everyone out of the front parlor so I could show off the sound system and my juke box, so you are welcome to come, Im not sure if you could get a quiet room to setup a mic to do measurements but your ears are welcome, although my tektons are in my bedroom and that is 100ft from the party so most likely quiet...