SVS SUB BETTER WITH LOW PASS FILTER OFF

I’m not 100% sure but it sounds like you might have been double ganging the filtering. You say your subwoofer output from your preamp or amp is 80 dbs, I think you might have meant 80Hz. If so, in most cases you would NOT need the low pass filter set at all on the SVS subwoofer itself then. The correct thing to do in this case is to either bypass it entirely (which you have found sounds better) or to turn the setting on the subwoofer as high as it would go, say 250 Hz or whatever, such that the slope of the crossover in the sub doesn’t interact with whatever slope is used by your preamp when it does its low pass at 80Hz. Anyway, that is what my old Klipsch subwoofer manual says to do. In other words, you’d only engage the sub’s crossover and low pass filtering if you were sending it a FULL range signal from your preamp. So, I’m just guessing here, but what you were hearing before might have been the crossover slopes of the preamp or amp subwoofer output interacting with the slope of the crossover in the sub. Removing the one from the sub filled in that "hole" you were describing, so it now blends better with your main left and right speakers.

Yes, of course 80 hz was my intention, and as usual for me its the most obvious stuff I miss. Glad I randomly discovered my mistake. Sure is much better. Now to put more Nano goop on my contacts! Any obvious advice on this sub I might have missed as well?

One things for sure… I need to see pictures of the yurt hifi room!

I would think your room would be almost 100% null free other than ground bounce. the La scala having very poor bass extension I am sure aids in the higher “crossover” point. 
 

I find my personal subs always lack a bit of detail compared to my mains above 100hz. I also find the sound stage with deep voices can get a little strange when using high crossovers. With that being said I will say a lot of subs play very clean all the way up to 200hz.  

I have the Arendal subwoofer and set the bypass at 10hz -15 hz above the floor of my main floorstander speakers that go down to 35hz. I read somewhere that 10hz above the low was a good place to start. I too switch the low pass 12hz filter off, as that works for me too. Saying that I use very little db gain, about 2.5db to get a very smooth integration. I agree doing it by ear even though I can do it through an app strung in my listening position is not as good as having some form of room correction, but in my case the room, is the room, is the room!

Glad you found the settings that work for you in your unique room.  Agree we need to see pictures your room sounds cool.  I have a pair of SVS SB1000 Pros.  My 2 preamp sub outs are also fixed with no adjustments available so like you I have the crossovers setting on the SVS app for each sub set to “off”.  It sounds great.  The one thing I will adjust is the sub volume as needed on the app depending on the music I’m listening to.  If the bass starts to overwhelm I’ll turn it down a few dbs or occasionally up.  Usually have them set to -12 db. As instructed in the SVS manual.