Well, good things to those who wait, or something like that. Just to put this on record for future reference:

After doing all of the things listed above last night (after a week of fiddling with this in other ways), I left both Control:PC and iTunes open and running all night and nothing had changed by morning at all. So I closed them down and did yet another reboot of TwinStores and Control 15 just before heading off to work, without waiting to restart either program. When I returned this evening and opened up both, ALL of the tracks had been copied to the iTunes repository.

So there you have it.

Sooloos C15, 2x2TB TwinStores, Meridian 808.5, BSG Tech QOL, Allnic L-5000, FirstWatt SIT-1s, Zu Dominance; Modwrighted Oppo BDP95, Classe SSP-800, Sony VPL-VW50 Pearl.