"I decided to upgrade my turntable in part because a persistent hum associated with the white cartridge wire..." Maybe you should have investigated that phenomenon further before investing in a new TT. White wire usually carries left channel "hot", assuming you are not running in balanced mode. So one question is what made you conclude that the white wire was involved in causing hum? If the left channel hot wire was in contact with ground, due for example to a short circuit inside the tonearm wand, that would usually result in no signal at all, not hum. But there are some other scenarios that might result in hum.
You go on to write, after purchasing the Denon TT, that, "I noticed one channel played very faintly. I checked the anti-skate, vertical tracking & stylus force ... nothing had any impact." Once those remotely possible causes of reduced gain in one channel were eliminated, did you check to see if the reduced gain could have been also related to wiring? If so, was the reduced gain in the L channel, by any chance? Anyway, since this problem occurred with the new Denon turntable, the scant evidence suggests that both the hum and the loss of gain might be due to an issue downstream from the TT/tonearm. Additional evidence to support that idea is your finding that when you switched to a Grado Gold cartridge, you now had equal gain in both channels but "terrible hum". In this process, have you checked your phono ICs or the input jacks on your phono stage? What I am getting at is that you charged forward, and continue to do so, without investigating the causes of the hum, dropout, and etc, that you are experiencing.
