I recently purchased some polk speakers. 2 RTI a7's for fronts, csi a4 center, and atrium 45's (free with purchase) for rears. I previously had a sony HTIB. The sound is definitly an upgrade from the htib, but I feel like I should be getting more bass and overall better sound. My receiver is a denon-889, and I use ps3 or denon 1904CI for playing cd's. I also feel like I have to really turn it up to get any bass or clarity to the music. I have the front speakers bi-amped, which i have heard that doesn't make that much of a difference. I still have the sub from the htib but didn't want to use it, or think I needed it with the A7's. Would adding an amp give me that extra bass or clarity that i am looking for? Or am I just expecting too much from these speakers? Are there any other suggestions or changes that i can make?