There is a file called XMCACHE.INI that you can edit and add the channels manually. Idealistically, there's a RELOAD button in RR's skin that should load your line up of channels from the receiver -- this has been reported to be somewhat flaky. I don't have a working XM receiver anymore, so it'd be very hard for me to "fix" that, but you still can try it (used to work for me).
As far as I know the channels on XM receivers are limited up to 255 ... there's no limitation as far as RR is concerned. If the Device supports it, it should list them anyway. This is instead of the Sirius receivers which are hardcoded to map only up to channel 255.
speaking of which...
i noticed on xm radio online, there are some new stations on 300-309.
There pretty good for being AOL radio.
its got new rock, hip hop, pop, indie, and a 1 hit wonders channel.
does the same go for RR on these high number channels?
The AOL stations are only for online listening. I did put an updated XMCACHE.INI file up there and I make this file readonly so it doesn't get messed up. Even if it's readonly RR is still naming my Christmas stations appropriately. It will not show the Christmas station right at startup but when the channel music list updates the station name is updated as well.
The Christmas stations are actually pre-existing stations. XM just created 'duplicate' channels in the recievers so they could group all of them together. But if you look around the dial, they're using the bandwidth of other channels.