MSC-400 has been flawless with RS-232 to an Outlaw Model 990 in my installation, apart from the MSC-400 having terrible grounding problems and introducing noise into my system when sending commands.

The fastest way to remedy an audio out of control situation is with MUTE or POWER OFF :)

If I were the OP and didn't need a device like the MSC-400 already, I would simply go the Xantech repeater route. In general, RF is a crappy technology for remotes and going through multiple layers to send single commands is a PITA. IR isn't used by everyone in the industry simply because it's relatively cheap.