It's interesting that your able to narrow down the problem frequencies.
You should be able to get a decent low frequency presentation at the listening position with one subwoofer by locating your rooms greatest mode using the Crawl method.
https://www.youtube.com/watch?v=AV3oLLMgS-M
During this test you might want to map out all your rooms modes in the event you add multiple subs.
For reasonably priced long interconnects check out Blue Jeans Cable or Monoprice. Good luck with it.
You should be able to get a decent low frequency presentation at the listening position with one subwoofer by locating your rooms greatest mode using the Crawl method.
https://www.youtube.com/watch?v=AV3oLLMgS-M
During this test you might want to map out all your rooms modes in the event you add multiple subs.
For reasonably priced long interconnects check out Blue Jeans Cable or Monoprice. Good luck with it.