I'm not sure that I buy this argument. It's the speakers job to reproduce the sound and their differences lie in how they're crossed over, balanced, etc.
It's the job of the source to supply the tones to the speakers so if your speakers are balanced to the high end, put a little bit of bass back in them at the source. That's why we spend all of this money on amps, etc.
Now, I'll grant you that my knowledge on hifi is pretty far out of date (I'm slowly updating) but the 703's look pretty damned capable to me and I'd epxect them to be able to reproduce just about anything that I want them to.
So... at the risk of asking a 'newb' question, why can't he just play with the bass balance on this amp to help him out?