Bryce, Thank you for providing more detail, I can now understand why you're having so much difficulty with this.
The key to diagnosing problems is to find the simplest setup that causes the problem, not just by switching inputs, but by disconnecting interconnect cables and unplugging units for the mains. Take the system down to a minimum that could show the problem (poweramp, it's PSU and the speakers only), then add components to the system one at a time...
Reconnect the preamp, then add back the CD player (& PSU),
Disconnect the CD player and reconnect the TT & head amp,
Disconnect the TT & head amp; disconnect everything from the Arcam 850, and connect it to the preamp (& PSU); then, one by one, add back each of the components that connect to the receiver.
Leaving the Arcam connected, reconnect the TT & head amp,
Then reconnect the CD player (& PSU).
This should give you a clearer picture of which components are interacting.