Replacement tubes for MF X10-D??

I've read that the X10-D can be improved by replacing the stock tubes. My problem is that I don't remember where I read it. Does anyone have experience with this, or know where I might find out more information??
The biggest improvement you can make with the X10-D is to remove it from your system, and sell it. The X10-D only does two things:

1. costs money
2. degrades sound quality

You'd be better off spending the money on a better source.
I bought a used X10-D that's using Sylvania JAN 6922/6DJ8 tubes... I haven't heard it with stock tubes, but the previous owner told me the Sylvanias, which can be found on eBay for <$8, make a big improvement. However, said tubes are pretty lean-sounding. Since my X10-D is in a second system, I don't listen to it much, but if I did, I'd probably replace the tubes with something richer sounding.
I've experimented with various tubes in the X10D connected to a Radio Shack Optimus 3400 portable CD player in a bedroom system. Even with the stock tubes, the improvements with the X10D are evident, especially in soundstaging. "Better" tubes will improve the sound of the X10D, its just a matter of how much money you want to put in this type of unit. Maybe Kevin at Upscale Audio can make a good recommendation for you. BTW, we experimented with the X10D in a friend's system using a Rega Planet with ARC gear. Although the X10D introduced a slight loss of focus and detail, the large improvements in soundstaging resulted in him keeping the X10D in the system.