I have very small main speakers. The crossover is at 100 Hz, which is the low end of what the speakers manual recommends (100 - 120 Hz). With an unlimited budget, I'd just get larger mains, lower the crossover setting, and build a shiva or tempest sonosub for massive, quality bass. I'm quite happy with the performance of my little speakers, though, and my budget is VERY limited. All I want to upgrade right now is the sub. I'm considering my subwoofer-upgrade options in the $400 range. A friend (I value his advice highly) suggests I get two pinnacle AC Sub 100's. The reasoning is that the 10" driver will be fast enough for the high frequencies, and I can place the subwoofers next to the front right and front left speakers to help make the directional sound (high crossover, enormous room) less of a distraction. I currently have to put the sub front-and-center to avoid that... the real estate there is limited, though, and a larger sub in that location would have a lower WAF. I also want to consider a DIY sonotube sub. DIY seems to offer better bang-for-the-buck. I also like the look of the tube subs, and the fact that I can finish them to match the room. Most DIY sonosub advice I find by searching here, though, is suited for 80Hz or lower crossovers. I want very accurate, musical bass. CLEAN bass. I'm less concerned with LOUD and less-than-30Hz bass. They would be nice, but in my situation I can't have it all. I've read that a Shiva in a sealed enclosure is fast enough to perform admirably above 80Hz. Is a sealed shiva tube a good match for what I'm tying to do? Maybe a 10-incher would be faster? Maybe TWO 10-inchers (two in one tube or two separate tubes for the high-WAF left/right sub idea?) Maybe one large driver for the lows and one small for the highs with a crossover in the sub? I'm really open to suggestions. What driver/enclosure combo do you think would be ideal for my HUGE-living-room, HIGH-crossover situation?