Check your BOSE manuals. Many of their speakers and subwoofers required a specific equalizer that was built-in to their amplifiers or supplied as a separate box.
Regardless, you’d need a 3rd party amplifier for the BOSE subwoofer because SONOS AMP’s cannot drive passive subwoofers.
Finally, ARC cannot drive 3rd party subwoofers. Only a SONOS subwoofer will work with ARC. A rear channel AMP cannot drive a subwoofer of any description.
---
If you use AMP for the front speakers, rather than ARC, you could use a 3rd party amplifier for the BOSE subwoofer. Currently, AMP in front will not support DOLBY ATMOS.
Than you ! Too bad in the set up a sub couldn’t be added just like the rear speakers. They are just 8 Ohm impedance as they were designed to work with other external amplifiers.
If a Port was added to the system with an external amplifier… could that be set up as either a subwoofer or as front speakers along with an Arc?
No. There will be no crossover and there will be time alignment issues.
ARC does not support extra L/R speakers.