One very obvious suggestion is to increase the bass volume as needed.
The following trick really works for the ST 130's Acoustimass so hopefully it will also help the 300's bass issue.
..You will rerun Adaptiq with a twist.
(Does not comply with Bose instructions. Do this at your own risk.)
1. Power down all components except your 300 SB, Sub and Surrounds.
2. Thoroughly cover the Sub with a blanket, especially very thick over front of Sub.
3. Run Adaptiq per manuals instructions.
The basis for this process is to require Adaptiq to output more bass through the sub. This may or may not help. If it does not help then recommend rerunning Adaptiq normally. I am not the creator of this trick.
If you try this DIY please reply with actual results.