Can it be used for 3.1 output only or will sound deteriorate if rear speakers are not used?
Hello glaurash,
Thanks for reaching out and welcome to the Bose Community Forums.
Only having 3 speakers will not deteriorate the sound quality from the speakers. You will just need to ensure that when plugging the speakers into the system you are putting them into the correct ports for where the speakers will be placed within the room.
If you need further help please do not hesitate to let me know.
Kind Regards,
Vicky W - Community Support