Nick, it shouldn't be assumed that your 503 wouldn't drive M80s adequately for your needs. It would certainly drive them at a reasonable sound level; the question would be if the levels you used and the dynamic range of the material you played would be beyond its capacity. If this resulted in excessive temperature and/or current the protective circuit in the 503 would simply shut it down, but there's no way to know if this would occur unless you try. A problem that might never occur shouldn't be assumed.
The speaker/line converter is similar to the circuit a powered sub uses on its speaker level inputs: a resistance in the tens of thousands of ohms is employed so that essentially no power from the receiver is used and just enough voltage to feed the audio signal information to the separate(or sub)amplifier. There's nothing that should result in any significant degradation. It seems a bit pricey at around $60 for the simple item that it is, and again it's suggested that you don't spend money on either it or the Outlaws until you've determined that you need them.
