50% is a little on the high side IME. You're getting enough volume for a trim setting but at what frequency and with how much distortion? You're definitely not getting anything at all under 35 or 40 hz.
That Klipsch sub isn't much more than a noisy boom box with a limited frequency band. I had a similar pair of ported 10" Klipsch subs too, before I got the SB1000s. I still have one right now in my office! Looking at specs they're virtually identical... I'm gonna say I'm very familiar with that particular sub and I know what it's capable of. In fact I am very familiar with both of your subwoofers because I've owned them both! You almost have as much space as I do too.
Going from a pair of Klipsch subs to the much cleaner sounding SVS subs really made it obvious I needed bigger subs. They played cleaner, but that also equated to less perceived output because the distortion was gone. Let that sink in-
I never noticed any distortion until it was gone. LF distortion is subtle and can go undetected without a reference. I really thought something was wrong with the SB1000s at first.
I know that either of those subs are struggling to pressurize that space and the driver(s) has to be dancing pretty hard, regardless of what the trim setting is. My AVR set a generous trim too, when I had the gains turned to 9 o'clock. Even then they were still lacking
to my ears, despite what my trim setting told me. There's a big difference between bass that's loud enough, and full, effortless bass that sounds good when it's loud enough. That's why I kept getting bigger subwoofers until I got it right.
In hindsight I could have skipped a couple of steps. I could have saved some money and been a lot happier a lot sooner if I'd just bought what was recommended to me in the first place. Some folks can be sooo stubborn tho...
