It's not a question of bigger amps. That won't help you unless the new amps have a wider range gain and/or sensitivity adjustment. You're already not using the full potential of your current amplifier. A bigger one would just leave you with more unused power.

You need to increase the voltage at the ampifier inputs. Either using an EQ or another preamp I suppose. But, you're sure that there aren't any other tweaks at the amp for sensitivity, right?

If you edit the songs, that could potentially be a lot of work. Plus if you play them later on different equipment you may find you don't like the way the sound when normalized/averaged or artificially ramped up. Your best bet (though not the cheapest in terms of $) might be to reconfigure the way you have things connected or get another amp that has a sensitivity switch. What about something simple like using the original Sony as a preamp for the empeg? It'll have to have AUX inputs or be adapted with an XA-107 or XA-300 module (I think at least one of those model nunmbers might be wrong (the letter part).. )

Bruno