No, Sonos hasn’t enabled adding two sub minis to a home theatre setup.  The reasoning that was given is that a single sub has more output that 2 sub minis, so it’s not the best option from a cost perspective.  Obviously, it is the best option for those who already have a sub mini.

Thank you. The FOMO logic drives me nuts but given hindsight’s 20/20 vision, I ought to have gone with the ERA 300’s. 

Question: Can I setup the 2 One SL’s in our home office (drive them off ther S2 app on my MacBook? and then add the 300’s to the home theater? Assuming it would cost $1.

The two Sonos Ones can be set up anywhere in your home, when you add the two Era 300s as surround speakers. The two Sonos Ones just need to first be separated from their use as surround speakers, and set up as another ’room’ in the Sonos software. Once that is done, you’ll have the capability of adding the Era 300s as surrounds. 
 

You don’t ‘drive’ Sonos from the app. The app is merely a remote control, which gives you access to the system running on the Sonos devices themselves. 

Thanks very much!