Bmatth:
I can not comment on the difference between Direct TV and full subscription sound, but I have a Polk XM Receiver in my home system and am very pleased. I first used the RCA connectors on the Polk unit but now have the Polk receiver routed through a Benchmark DAC. Sound quality on Jazz, Instrumental and Classical stations I find to be very good; good soundstage and clairity, above FM quality but somewhat below CD's. On Rock and similar types of music XM has the same problem (or same theory) as FM as the sound quality is compressed and not very appealing. You could try a Polk unit and full subscription and if you are not pleased return the unit / cancel the service.
I can not comment on the difference between Direct TV and full subscription sound, but I have a Polk XM Receiver in my home system and am very pleased. I first used the RCA connectors on the Polk unit but now have the Polk receiver routed through a Benchmark DAC. Sound quality on Jazz, Instrumental and Classical stations I find to be very good; good soundstage and clairity, above FM quality but somewhat below CD's. On Rock and similar types of music XM has the same problem (or same theory) as FM as the sound quality is compressed and not very appealing. You could try a Polk unit and full subscription and if you are not pleased return the unit / cancel the service.