Firstly, recordings do vary - some will be quite full sounding, some quite punchy, some smooth and laid back, some bright and harsh etc. Do make sure what you're experiencing isn't just differing sounding recordings. If you have some recordings that sound great, then there isn't an issue.
If it's not down to the above, we can look at the system. While changing the pre will improve your system quality, and changing the power amp will improve grip and headroom, I'm not totally convinced that either of these changes will solve your issue. The NAP200 is a great power amplifier, and it will be a punchier sounding than a 150 in any guise, but is likely to sound leaner in some ways as it's more controlled and neutral. I'm guessing this can only add to what you're experiencing, even if quality is improved.
Naim tends to be a slightly leaner sound than many other manufacturers, so don't expect the big meaty bottom end that some amps have - this is where they get their speed from.