Question

arc ultra and sonos sub is so underperforming

I have a sonos sub and sonor ultra with Sony TV , but the performance is soo poor, especially the sound. Any suggestions

Given the lack of information in your post, some generic notes:

make sure your Arc Ultra is connected via ARC or eARC, and not TOSLink
make sure the content you’re watching is Atmos, or Dolby Digital (not YouTube, which is mostly stereo
make sure your Sub is properly bonded to your Arc Ultra
make sure CEC ( which Sony likely calls something else) is turned on
if you have surrounds, make sure they’re bonded correctly
if you want, go into the settings for the room that has the Arc in it, and turn on both Loudness, as well as turning up the Sub.
call Sonos Support to discuss it, rather than telling those of us in the public, they have access to data we don’t.

When you speak directly to the Support staff, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.

Bruce