thomas, I love mijostyn. His system is terrifically satisfying. Judging by that system and his unbelievably well appointed wood working shop I'd say he has a financial foot up on most of us here. I know I'm envious.
Yes, you can absolutly have excellent bass reproduction at the listening position with one subwoofer.
To the left of the four white RCA outputs on your HGC. The upper two RCA's are labeled L (Left) and the bottom two are labeled R (right). The bottom R output will connect to the red (Right) input of the subwoofer.
Below is the Velodyne SPL-R series Manual
https://www.velodyneacoustics.com/pdf/spl/SPL-UltraSeriesManual.pdf
Does the layout on the Front Panel Features of your SPL include the (4) MIC input as in the drawing on page 5 of the SPL-R Series Manual?
There are two different looking Remote Controls both have the same function buttons as the one pictured on page 11 of the SPL Manual. Do you have the Remote Control?