Not sure that upgrading cables to a sub is going to produce a huge improvement...since your initial cables are decent to start; but I could be wrong...let us know....
We have some similar pieces; I do love the VAC tubed preamps...but the biggest step up for me in sonic enjoyment and quality was to switch to DSD capable DAC; omit the CD player; and rip all my music CD's onto a hard drive; and then up-convert to DSD....I had a decent Ayon CD5s, and the switch to Playback Design PS5D was incredible.
Keep your current VAC preamp; and replace it with a dac that can up-convert usb files to DSD, several makes out there; the MSB analog DAC, EMM, Chord, Playback Design, and I think Esoteric...
If that move doesn't float your boat; then try the upgraded VAC pre....we both are pure digital people; with no TT...and using our rig for combined two channel/HT.
I'd love to hear more about what the Novum PMR device did to help tune your room, and how you are liking it...
Glad you are enjoying your set up; and the new cables....