My current Sub is located front middle (mostly due to having four cats) and I’ve added a little gain, but adding a second sub is a good idea, the SV1 is quite musical and nimble but is maybe lacking oomph and maybe needs a big brother.
That’s almost never the best location in room for optimal subwoofer performance. Your sub goes down to 21Hz -3dB, and I suspect you may not be getting all it’s capable of so before adding another sub I’d work on better placement (if at all possible) and optimizing the sub’s settings as well if you haven’t already done that. If you have placement flexibility I’d use the crawl method to find the spots in your room where you’ll get the best bass in your particular room, and here’s a link for how to do that…
https://www.audioholics.com/home-theater-connection/crawling-for-bass-subwoofer-placement
Once you find the right placement here are some straightforward and effective instructions on how to optimize sub settings in case you haven’t already done something like this (these are from Paradigm who makes pretty good subs)…
Set the pre/pro tone controls, equalizer to FLAT and turn off any LOUDNESS adjustment. Grab a friend or wife...but not a friends wife....
1. Turn the Subwoofer Level control completely counterclockwise to its minimum; 2. Turn the Subwoofer crossover frequency control clockwise to its highest frequency (i.e. 150 Hz). 3. Set the Phase Alignment Control to 0°; 4. While you listen to a bass music or video selection in your primary listening area, have an assistant turn up the Subwoofer Level control until the subwoofer can be clearly heard; 5. Have an assistant try the Phase Alignment control until you hear the most bass. Your subwoofer and front speakers are now in phase. Do not change phase alignment again unless you move the subwoofer or the front speakers to a different location in the room or move or remove large items of furniture or room furnishings (i.e. carpet, draperies, etc.) 6. Turn the Subwoofer level contol completely counterclockwise to its minimum. 7. Turn the Subwoofer crossover completely counter-clockwise to its lowest frequency (i.e. 50 Hz); 8. Slowly rotate the Subwoofer Level control until you match the subwoofer output level with the level of your front speakers. Bass should be clearly audible, but not intrusive; 9. Slowly rotate the Subwoofer crossover control until you hear the best subwoofer/main speaker blend. If the sound is too ‘thin,’ you have not set the frequency high enough; if the sound becomes ‘boomy’ you have set the frequency too high. Adjust until you find the most natural balance. The sub should not draw attention to itself.
Your interconnects/cables seem ok, and I wouldn’t bother with bi-amping. Hope this helps.

