I was always told that it was high capacitance that caused hi frequency loss. The original TASCAM LO-CAP cable made a significant improvement over typical hi-fi shop/Radio Shack interconnects. HOSA was Fostex's answer to Tascam's cable and proved to be a worthy competitor.
I've used HOSA cables and have had no problems with them. They pass signal without high frequency loss and are very robust. FYI - I think you've underestimated the number of cables you'll need. And do yourself a favor by laying your 38 on it's back. The capstan bearing will last longer and...
Bad tape with sticky shed syndrome most likely. Toss it. Clean you entire tape path and use newly made tape. Forget NOS stuff. It's a false economy that could possibly ruin your machine.
It's not just the "shed" that does damage. Sticky-shed tapes are extremely abrasive, so much so that heads can be ruined. Motors aren't too happy trying to pull that stuff either.
I would never hang any musical instrument on a studio wall because their sympathetic resonances would be problematic. IMHO, the areas to address are the floor, the creases where surfaces meet, and the window.
Original Great River MP-4 with direct outs, original Spectra Sonics 101 w/502 eq's, Deane Jensen Designed dual-opamp, Great River MP 500NV. All are squeaky clean except for the NV.
I would try all of the following: Turn graphics acceleration totally off. Don't let windows decide performance. Click the "adjust for best performance" option in settings. Set Audition's compatibility to your previous OS. Also, use a different drive than whatever drive your os and programs...
I have the 32 input version of this board. My only complaint is with the so-so performance of the mic preamps. They're quiet enough but are rather "soft sounding" due to poor transient response. Because of this, I use my outboard units for everything.
How hot does the deck plate get while the machine is in operation? If it gets warm to the touch, I would not cover it up with anything. If you have a remote, baffle the machine off once tape is loaded or move it out of earshot where the mics can't pick it up. If all else fails, get some...