I have been looking at refurb. Marantz's and I can get the SR7200 for $499. The 7300 is $649, the biggest difference I see is the 7300 has an RS 232 port. I know this port is for upgrading, so, does that mean in the future if someone comes out with something like a 8.1 EX II DX THX etc. etc. all I would have to do is download and I could run to the new format? Also, I can get the 7300 OSE which is supposed to have a better power supply but it is $849. Is that worth another $250? Would there by any differnce in sound between the three?