Luxman leaves me wanting

LTA is wonderful stuff because it is very neutral as tube gear goes.

These days, in the land of digital processing and streaming, Neutral hardware is always the best place to start, like a sheet of white paper. Then add some color separately as needed via Roon DSP or any other means you see fit.

Things were different back in 20th century analog olden days when hardware did it all. Nowadays you want neutral hardware then let the software paint the picture your way. Being stuck in the past can be a big and fairly expensive handicap. 

@steverrino 

I had the same problem! I tried to power a pair of KEF Reference 1 Metas with a 590AXII. I had absolutely no bass and a terrible midrange. It was so bad, I thought the integrated was broken. I brought it to the nearest dealer, and we confirmed that the amp did not have the power to drive the baby KEFs. I upgraded to McIntosh MC611s, and the bass/midrange is jaw-dropping. 

Your Super Nines are not as difficult of a load to drive as my KEFs, but I think you need far more power. Even the Luxman 509x did not have enough juice for the KEFs. The M10x was a different story, though (glorious sound).

If you know someone that can lend you a decent pair of subs, I would try that first. With a budget of 8k its easy to make an expensive mistake. But if you just want some ideas that might work for you, here's a few. BAT, Sugden, Pass, Sim, YBA. Even though they are all very good, I still wouldn't buy anything without trying it in my system first.  

Thanks for all the helpful suggestions. I’m pretty familiar with a lot of gear talked about on this forum, but haven’t heard of Sinthesis. I will look into them.

i do use Roon, but have not tried the EQ filters or room correction - but that’s a great idea. I’ll start there. I have thought of adding a tube pre to my L590AX-II, and am glad to hear that hsounds had good results doing so.

Two years ago I wanted to down size a little by going from separates to an integrated amp. After a couple of months of research, it was down to Luxman and Hegel.  I ended up buying the Hegel H390 to power my KEF Reference 5’s. The Hegel is quiet. The Hegel images well and gave me good separation. The bass is full, the midrange is clean and the high end is actually very pleasant as well. 
Hegel just replaced their flagship H590 with the H600, so they are discounting the H590’s to about the same price as the H390, until inventory is gone.