what to buy under $500 bi wire spkr cable

What speaker are you using. Perhaps the problem isn't the speaker, not the cable.

It is not the cable although the terminations may be corroded.

Just to be certain that nothing simple is being overlooked, are you sure that the + and - connections to one speaker are not reversed, relative to how the other speaker is connected? A reversal of relative phase would probably account for both of the symptoms you are describing.

Regards,
-- Al

I had the Monster 2.4, very similar, and before settling on the AQ Oaks, tried the AQ Gibralter. The Gibralter had much fuller, lower, focused bass, lower noise, greater transparentcy, richer mids, more extended highs, etc. Used can be had at your price point. Sounds like a schill right, nope, and I don't have any for sale either.

I doubt it's your cables, and your speakers are capable of good bass so I would look elsewhere.