I have a Polk, too, and I never listened to it because the sound was... not good. Later, I connected its digital output to a Mc MDA-1000, and sure enough, the sound was greatly improved, but still really lacking compared to the average CD.
I'm skeptical that even MD can turn a sow's ear into any kind of silk purse, as the digital signal just isn't susceptible to much improvement. Too much info has been lost in compression for even a first-class upsampling DAC (the Mc is 24/768) to reconstruct.
Thus, I'm wondering if anyone has actually heard either of these expensive units?