Voice and instrument image bunched in the middle??

Of course this kind of thing is very dependent on how material is recorded and will vary widely from recording to recording. Hopefully you have a frame of reference for how the recordings you are testing with should sound? If not, getting the right reference recordings to test with would be step 1.

(1) Agree with Mapman .... Quality of the recording itself will impact your enjoyment.

(2) Which leads me into the next obvious factor: the performance / resolution capabilities of your system, particularly your source , may be an equal or greater contributing factor ... both good and bad perspective.
- The "bad" is intuitive.... Limitation or compromises on resolution on what's there in the recording
- The potential "good" aspect manifests itself wherein a superior source and accompanying system highlights the poor resolution / mastering / other limitations in the recordings re: Point #1 above.

It sounds like you are listening to a mono recording. If the recordings are old this may very well be the case. One thing you may want to try is to reverse the speaker cables on the binging posts of just 1 speaker and see how that sounds. If you are biwiring, switch both, but just on 1 speaker. Listing your equipment would also be a good idea.

You do not describe your equipment so it is hard to understand what is going on. It can be a tweak for speaker placement, changing a capacitor in the preamp, etc. Have you heard the same recordings in a different system that had different results?

Make certain that your speaker cables are each going to the correct speaker. That has often been the cause of the problem for me.