Here's my opinion:
In using 4 towers: In the words of Bro Chito, medyo overkill pero ang sarap nun. Remembering the fact that digital movie sources offer full range outputs in all 5 channels, the entire sound spectrum from 20 ~ 20 KHz, so you'll actually hear all the details from the rears too. Although, I don't think mahihirapan ang receiver mo, unless you play it at full blast. Usually, amps supply just around 5 to 10 watts of power to each speaker at normal listening levels. I'm sure the amp can handle that. Read more of this at the "Pioneer 100 wpc...." thread. That info is, of course, provided by the master, Sir AV. On the assumption that the speaker has a sensitivity rating of 89 dB per 1W/1m, that means the speaker is 89 dB loud at a power input of 1 watt when a listener is 1 meter away from the speaker. Then a power input twice of that would add 3 dB to the volume level, so at 2 w, it's 92 dB loud, then at 4 w, it's at 95 dB, at 8 w it's at 98 dB, and so on and so forth. As far as I can remember, an average human conversation is at around 60 dB, a jackhammer at around 100 dB, that's where hearing damage actually starts, if I remember correctly. So, as I said, at normal listening levels, 5 ~ 10 w lang ok na, unless of course you like bleeding ears from ruptured ear drums. So the power issue here is not really an issue. It's more of the redunduncy of your speakers. It may not be necessary and practical anymore, having a good sub and speaker configuration would be enough. But, different strokes for different folks.
Bro fweyd,
The DQ12 is actually a front firing sub so, it's pretty accurate as far as sub enclosure designs could go, a sealed enclosure being the most accurate but requires more power. So try mo DQ12, you might like it, I have this one at home too. The USAudio US512MKII is the one that I'm referring to when I said less accurate ang bass nya since bandpass ang enclosure design nya, but this is a very powerful sub, and I have this one at home too. Audition, bro, that's the fun part.