The sonicblue website makes mention of two types, the RM2XS and the RM4XS. I can't find any info on them on the Sony site.

You can get at least one of them at Crutchfield if you're in the US. I don't know the difference between the two.

Also, will I need to install the tuner module to be able to use those remotes?

Yes.

Is there a way to make those stalk controllers work with the empeg unit without having to install the tuner module?

Yes, but it requires building your own serial-port interface with a PIC controller and blowing an EPROM with code. Since you already have a tuner module, that's much easier.