I agree go the sub-10 or sub-12 route. It sucks you had a bad experience, but I can assure you they are quite something else..esp. the sub 12...that sucker has some grunt. However just to clarify, the 4.1's in no way reach 29 hz, not unless at an EXTREMELY low volume, or with a tone of port noise. They are good to abut 35hz in movies, and about 40hz in music. The sub can reach around 105db at max volume, around the ports tuning freq. which is I believe 50-53hz.
MD, even though it's pretty much agreed that the 4.1 has the easiest going slope of all promedia systems (basically, they leak as far down as the 80hz area at higher volume, reason why the midbass drivers in the 4.1's always over excursioned at 100db or more). I'd still go for a seperate reciever or what not. Better quality, more freedom to do whatever, and would run cooler, more efficently.