Well, that does depend doesn't it? I won't say not all the available tracks in HDTracks come from analogue tapes that don't have resolution. In fact, I'm actually not certain what that means in the first place. I know resolution in digital terms but resolution in analogue terms, that's new to me.
Anyhow, if most of the tracks HDTracks sells are from SACD converts, it'll depend on the recording masters of the SACD in the first place. e.g. beliefs are that Norah Jones' "Come Away With Me" was supposedly from Redbook upsampled to SACD so no benefit there. But OTOH, something like Dave Brubeck's TimeOut may be a different story since the original is from analogue tapes when mastered to SACD.
Well we are getting onto another subject here but maybe not since the DX100 is designed to finally use some of the high resolution recordings. With regards to SACD, I have a few hundred and a number have no better sound quality than a red book. Often a recording is done and then run through the board with signals getting squashed and there goes the dynamics and soundstage. I like uncompressed and unprocessed and correctly miked recordings but this isn't often done.