Seeking opinions about phono specific interconnects

IMO, for you, the best solution would be a multi-band equalizer.

I would start with an inexpensive one, if happy with the effect, keep looking for one that fits your system best and perhaps higher quality

If nothing else, you will have learned which frequencies need taming for you, that helps when evaluating models of cartridges/cables/phono stages/any component you might consider in the future. 

Does your preamp have two outputs? Put eq between preamp/amp after riaa eq has occured.

Do you have a tape loop to try an equalizer in/out of circuit?

here’s a dbx 31 band, free shipping, 30 day return

IF you like it, remember it is used. I would buy it and the Rockwell. IF the DBX is totally quiet, then keep one, return the other.

after using a couple in the past, I realized: t's a mistake to try and get perfectly flat, messing with each band. Just find the ones that make a difference for you.

You couls get an inexpensive sound meter, and a good CD (not LP) with individual frequencies, tripod mount, seated ear level,

you will learn more about your speakers and their interaction with the room. you might use the equalizer to solve a peak or dip that is occurring 

This one is most tempting, flat bypass; 4 memories; spectrum analyzer, tape loops.

I would still buy/keep/return the NEW Rockwell.

originally came with both a MIC, and Remote Control, you would need to confirm with seller, they might not even be aware of those.

OP's Hearing Problem will not be relieved by refining VTA, .....

"I'll add that I am exceptionally sensitive to higher frequencies due to having Hyperacusis"

Equalizer Inputs/Outputs: check,

Some, like the Rockville have XLR and/or MIC jacks, no RCA. for those, XLR/RCA adapters can be used

Others, Like the BSR have RCA in/out