soundhound - Are you thinking primarily of home theater receivers here as compared to older amps, integrated amps, and receivers? I'd certainly agree when it comes to the typical receiver power amp section, as the "4 ohm" or "6 ohm" switches you mention attest to. On the other hand, I've been under the impression that separate power amps from companies like Outlaw, ATI, Rotel, Anthem, etc. are built robustly enough to handle lower impedance loads without issue.