Even though B&K receivers pack a really nice amp section, adding a B&K outboard amp(200w/ch) has to be an improvement. Your 307 puts out 28 amps of current(peak to peak) while the 200.7 puts out 75 amps of current(peak to peak). That equates to over 2 1/2 times the amount of current to drive low impedence loads if need be. I am not speaking from direct experience with your exact setup but from the data it sure seems like it would be at least a slight overall improvement. I say do it. I have a 3 channel B&k Ref. 4430(200w/ch) amp and it improved my setup by leaps and bounds.
Bill
Bill