impedance question

Hi I'm trying to understand ohm's and power. My b&k 200.5 is rated at 200 watts per channel at 8 ohms and 375 at 4 ohms. Now some of my speakers are rated 4 ohms and some are rated at 6 ohms. My question is does the amp just feed the power differently to each speaker accordingly? ie, 4 ohm speaker will receive 375 watts and the 6 ohm somewhere between 200-375?

2nd question is i had my sub woofer wired parrellel to my mains, everything seems to be working fine but I just read that I really put a load on my amp by dropping it to 2 ohm? is this correct? Is this a bad thing to do? I don't know how else to wire my sub because for some reason my rca sub output on my receiver doesn't seem to work. any suggestions?