I'm curious what Outlaw had to say about using a 2-ohm load. Beyond stability issues, that's a big increase in output current, and unless you're really careful about how high the volume control gets cranked, you risk blowing the power amp, either output transistors or the power supply. I have used parallel-connected speakers in a center channel before for the 6 dB of additional output this provides, but my setup used 8-ohm speakers. Unless you are looking for the extra output of a parallel connection, a series connection of the 4-ohm speakers is much safer. Sound quality should not differ between a series and parallel connection, although you could experience some noticeable sound difference between a single and dual speakers due to comb filtering between the two speakers depending on their location to one another.