I don't think an MR-88 is the answer to your issue. The MR-78 is one of the best FM tuners ever made. What sort of reception problems are you having, and did they always happen in this location? The MR-78 is certainly a classic component, but given its age it may benefit from an alignment. Are you using an antenna appropriate for your location?
As for Sirius/XM, you'll get better fidelity from the online stream than you can from the satellites. It's still not hi-res, for sure, but I find it a-ok for casual listening. I stream it from an iPad using digital out into my DAC.