Would appreciate feedback on logic

I've connected all my speakers with Radio Shack 12 ga zip wire. OK, the speakers make sound and I like the sound. That's all I can say at the moment. My listening room has hideous acoustics with small area, one side wall concrete the other side wall opening onto a larger open space, speakers forced to be inches away from back wall that's concrete block, poured cement walls elsewhere, thin pile carpeting on floor (basement), etc. and to top it off there's a huge steel home gym in the middle of the room. Now, I'm interested in seeing if a change in speaker cables may benefit my system. I reached out to a couple of manufacturers who offered home trials and was very transparent regarding my current environment. No cable manufacturer wanted their products trailled in the listening environment I described. OK, here's the logic question - good or bad, if cables made a real difference, would that difference not be detectable more or less in any listening environment? I have 5 pages of listening notes focusing on a set of reference music from Bach to Judas Priest, describing specific passages or features in the piece and what I'm hearing. If cables made some difference, would not a difference be detectable? I have a $700 budget for speaker cables and am not interested in acts of faith here. I'd rather make my own from Cat 7 ethernet cable than drop $700 on vendor attestations.

I'd be interested in knowing if my thought process on this is in error, and if it is how I should approach speaker cable auditioning.