I would try the Stereophile Test CD #2 which has the most test tones of the three, with #3 being a close second. Don't have any experience with other test cd's or online resources. I would look at a phase tests first, out of phase speakers sounds most like what you're describing. Next a simple frequency sweep, one speaker at a time to check the drivers. I know you're looking at the cdp, but don't discount the speakers as a problem, and they have a bunch of CD tests as well. Disc #2 has a music articulation test that is the most revealing cut for total system clarity that I've yet run across, but you really need a baseline to make it effective.