Help me pick some new or used speaker cables

Just bought Worlds Best Cables with a 8 gauge bi-wire arrangement on spades. Ran me less than $300 and sound great. Had heavy Monster M cables on from the 80’s and they weren’t terrible, but read a few good things about WBC and for the money they worked out fine.

There are some great options for speaker cables mentioned - I'd also consider Nordost. I've been very impressed with them as with Transparent.  

I've been very pleased splitting my cables - Shunyata for power and Kimber for speakers/interconnects.  

Some great advice thus far. I’d add that buy used because if you don’t achieve what you seek, you can sell them for what you paid. If you buy new, support your local dealer and try them in your system to know 1st hand if it’s the right combo.
 

The cables I’ve liked the best are OCC wire to start with. Ocellia are sublime, and should put you in the right place. If by chance you’re running Sylvania 6SN7 in the MW LS100, get them out in favour of a different tube like some 40, or 50’s RCA. (I had a LS100)

I have tried most of the "high end" name brands and once I found Silversmith Audio Fidelums.....game over.  Well with in your price point new.  ONLY cable I ever purchased that sounded great right out of the box and simply got better with hours.

Better speaker cables, yes!

I may have missed reference(s) to room acoustics on this thread, but certainly worth looking into (if you haven’t already).

Congrats on thinking outside the box with the T-7 mods. Typically "mods" will calm down certain ranges due to incorporating better materials, connection/termination methods, attention to sympahtic resonances, etc. If all else fails you might consider having a conversation with your "modder" about this. I’ve found that bumping up the tweeter crossover point ever so slightly can remove a little hardness.