Have you thought if switching your B17 from the FX 7.3 to the 2.1? It won't be absolutely probative, but if you like it better than the new one, you can have some confidence that it's a break-in issue.

Are your bars lower than your saddle on the 2.1? If so, you may never get comfortable on the B17, although many people get good results from tipping the nose up slightly, though that's counter-intuitive. Or just get a Selle SMP.