Quote:
All else being equal, does this configuration result in better sound quality than connecting both pairs of speakers to an integrated that can handle the A/B switching?

All else being equal, the only thing that matters with power amplifiers is their frequency response, noise, and distortion. It does not matter if each amplifier is encased in a separate chassis, or shares a power supply with a preamp and tuner, etc.

--Ethan

I think his question is aimed more at whether a single integrated can handle powering two sets of speakers or whether he should get another amp to assist the integrated.

Both setups can work fine. If the integrated does not have enough current delivery capacity to power both sets of speakers simultaneously you will have problems. This will depend on the particular integrated amp and the particular set of speakers.

The problem arises because the integrated amp will have its two pairs of speaker posts wired in parallel. Thus when the two speakers are active at the same time the total impedance drops a great deal, making it harder for the integrated to drive. If the speakers have a high enough impedance - or the integrated is beefy - this will not be a problem however.