I just recieved my CD-7 back from ARC with the upgrade. Will was right on in his assessment.
I only had time to listen to a few "cuts" before I had to leave, so anything I say here was with less than an hour on the player. Its operating on "repeat" until I get home tonight.
The improvement is NOT subtle at all ... in fact, from my limited time listening today, what occured to me was ... this is like going from a mid-grade Grado cartridge to a very good moving coil. In comparison, inner-detail is much improved, like hearing around the notes of a classical guitar. Dynamics are much more explosive ... try the Jessica Williams "Live at Yoshi's" piano trio, both Vol-I and Vol-II. Amazing.
My contact at ARC tells me that the modded CD-7 gets you about one-quarter to one-forth of the way to a CD-8. All I can say is, the CD-8 must be something speciall indeed.
I'd recommend the upgrade mod to anyone who has a stock CD-7. Original owners get the mod for free.
Take care guys and happy listening.