Until the AR500 came out, all of Spektrum's "full range" receivers had at least two separate units, a main receiver and a remote receiver, each with two antennas. All of the DSM2 park flyer receivers were much smaller, lighter, and had only a single unit. It sounds like the full range units had two antennas AND a separate receiver for each of the DSM2 "channels", while the park flyer units simply have two receivers in one unit, with a single antenna & receiver for each DSM2 "channel".

I've read that Spektrum's main concern with using DSM2 park flyer receivers in larger planes was the lack of signal path diversity. The full range receivers placed a receiver for each DSM2 "channel" in two separate locations, so the likelyhood of both channels being blocked by the engine, battery, etc., was very low. The park flyer receivers have both "channel" antennas right next to the main unit, so they are more easily blocked by engines, batteries, etc.

Now, with the AR500 receiver, it seems they've discovered they can get this signal path diversity for a full range receiver with a single unit and only two antennas, one short antenna, and one longer one that can be place remotely via coax cable.

I'd bet that the internals of the AR500 are almost the same as the AR6100, except for the remote coax cable antenna.

Anyway, with the AR500 being only $10 more than the AR6100, and not much larger, I think I'd prefer to get the AR500 for a little more range & piece of mind.