Set Bitstreaming back to Yes (DSD). This takes almost no CPU power, and my 2014 Intel NUC with 4GB RAM (so "weaker" than yours) has no trouble (and had no trouble with version 27) bitstreaming DSD.
If I have read the thread correctly, things were working fine and suddenly with no software changes you started getting cut outs. This will probably turn out to be a hardware problem. Have you tried different USB ports for the external drive and the Marantz? Does the computer put the USB ports to sleep to save power? (Disable if yes.) Are you using a special USB cable to connect the Marantz, or do you have a so-called de-crapifier in the USB line? If yes to either, replace with a standard USB cable with no de-walletifier. If you're completely stumped, trying cleaning the fan intakes for the power supply and CPU cooler.