Do you hate the tinny speakers in boats or just in general? I just pulled my Polk db675's from my truck because they were too bright (tinny) for my tastes but I really like them in boats. Same applies to Infinity Kappa's. On the other hand I replaced my truck speakers with MB Quart's that sounded flat (dull) in a boat. The MB's sound great in my truck.
MB's and Boston's tend to have softer high's then Polk's, Infinity's, Kicker's, Sony's, etc. You could also go with Cadence, Morel, Dynavox, or other high end speakers suitable for classical listening. The difference is most notably a flatter high end.