A:AnswerIf your current sub is the Sonos sub yes. You can only use the Sonos sub. Sonos is currently working on a smaller Sonos sub . That will be perfect for the Sonos Beam gen 2.
A:AnswerAny hdmi cable that mention “ARC” capable with work up to many many feets .
If your sources are 4k , them get them ARC 4k capable and you will be ok .