Thank you for your post and welcome to the community!
Allow me to explain, there is no difference between the Bass module 700 and the Accoutimass 300, the product was just renamed when we brought out the SoundBar 700.
This will explain why, in the Bose music app it is named as the Bass Module 700. So, if you choose to add a second bass, you should get the Bass module 700 to add to your system.
I hope this helps! Have a great day!
Jessie - Community support
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