Get the speaker/amp match correct and the majority, if not all, of your problems with their sound will be ameliorated (within the capabilities of the speakers). I suspect the Nakamichi isn't delivering enough power into the bass frequencies relative to the mids and highs, which makes the bass sound weaker in comparison.
Attempting to match a preamp for speakers is the wrong approach, and will not fix the problem, IMO.
You could try something like the Portal Panache integrated amp, which sells for around $700-$800 used.
Attempting to match a preamp for speakers is the wrong approach, and will not fix the problem, IMO.
You could try something like the Portal Panache integrated amp, which sells for around $700-$800 used.