[Chrisbee]

I like the use of a stereo amp + sub and I am still using stereo with my 4 x 15" IB using an active stereo crossover on the main speaker channels.

Adding a 3.1 processor for center and rear channels for films makes me a bit of an HT dinosaur.

The obvious advantage (to me at least) is higher sound quality.

Place your sub between your main speakers and don't take anything for granted.

With my SVS cylinder I used a 60Hz crossover despite my 40Hz floorstanders playing fullrange.

Try REW to see what is really happening to your frequency response at the listening position.