Here's my situation. I have the M4 mesh in my home. This doesn't support the higher speed of 800MPS I have coming in and is causing quality issues in the signal for streaming (xfinity). I can upgrade to the M90, which is fine, but can I also use my M4 without conflict for low latency applications?  I assume yes I can use it but will it cause issues with the X90 network if I go that route?  Also, I have WiFi extenders and they're really not that great...could be a similar issue in the inbound speed and not handling that. So, if I bought the X90, which has two units, can I get an additional unit and add it to the network to expand the coverage even more. So X90, 2 units, +X90?  Or is there a better solution?