hifi engine

Mixed speaker impedence

Running, at times, a Sony STR-D1090 or a Sony STR-7015 or a Scott RS250. Main turntable is a Marantz 6300, sometimes a Sony PS4300. Speakers are a pair of Audio Research AR-215 from the mid-70s and a pair of Bose 410s from the early 90s. All receivers are capable of powering two pair of speakers, which I am doing (A + B). Nothing fancy but everything sounds great in my little record room. It appears that the Bose have an impedence rating of 4 ohms and the Audio Research have a rating of 8 ohms. Current and usual configuration is the STR-D1090 and the Marantz 6300.
I am not an audiophile but a serious vinyl collector and want to get the best out of the gear I have.

1) Anyone aware of a setting on the D1090 (or any of the other receivers) to acknowledge a pair of speakers at 4 ohms and another at 8?
2) Does it mattter? Will they all work with mixed numbers on the speakers? Nice sound in this configuration with the ARs more pronounced. Am I really hearing what the 410s are capable of with this mix-match of impedence ratings?

Appreciate hearing (no pun intended) from those tech guys that can dumb down this miss-match impedence issue. Thanks.