Echoing the above, seems like you have a really good start. Regarding the dedicated lines and interference, running the lines seprately and not bundled is of course a good thing to do. You may also want to consider running shielded 10g Romex - I had pretty good success with it (had it cryo treated by Audio Excellnce as well). I have also had success with Cardas in wall cabling as well.
Also, something to consider - the best step I have ever made in reducing noise via the electrical setup is using a 10' chemical grounding rod buried in bentonite clay - massive improvement for a reasonable cost in view of high end audio. There may be some hassle in rewiring it to you new audio outbuilding when completed, but I would suggest it is worth it.
Best of luck.