Spectrum will provide a modem only and let you use your own router and AP, but if they won’t budge on anything regarding it that’s probably not an option.
What exactly are you trying to accomplish though? What will your friends being doing with your NAS? Spectrum doesn’t have great upload speeds so at best they’d get slow downloads and at worst it would make your internet unusable with them maxing out the upload.
I don’t know why I never thought to just try it out before. Popped in a 10GBaseT module and switched over my mac studio and sure enough, it’s running just fine at 10Gb on a cat 5e run.