Changing out speakers is not going to solve high frequency reflection issues. If you have a lot of flat bare surface, you should consider some sort of treatment. It may be as simple as carpet and some wall hangings at first reflection points.

If this is a music only system, you don't need a huge sub. A capable 10 incher will reach down into the 30Hz range quite nicely.

Fred

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Blujays1: Spending Fred's money one bottle at a time, no two... Oh crap!