LUXMAN L509X VS M700/C700U

The  C700 would be the natural addition. One other option would be the Luxman CL 38U-C tube preamp and match it w/the 700U. I have the Cl38U-SE w/a Bryston amp and it's an excellent combo.

What do you guys think of 509x 
it has the c900 pre amp 

also does 509x also has the first few watts as class A like M700u 

Cl38uc did it soften the sound ? Did u compare that with c700u 

Not so much soften but a smoother less digital sound. All the details and dynamics were still there. I also have a Luxman PD-171A TT hooked up to the preamp and the all tube phono is excellent. Has 4 steppe transformers. 2 for MC high and 2 for mc low. If you have a Luxman dealer nearby it would be worth checking out the tube solid state combo..

Get a CL-38 vacuum pre to pair with solid state amp. This is commonly done to sweeten the sound of a cold SS amp. This may also tone down those horn tweeters on triangles. 
Alternatively, Sell the m700 and get a full tube set up, MQ-88 and CL-38. Paired with your DA-06 you’ll have a world class system that would suit your triangles. Sound of tube separates, IMO would be sublime with bright triangles.
Keep the m700 so you can compare before you cull it. Get the integrated if you have space limitations. 

Neither Lux 700 is the 900 series or the 509x includes 900u pre-amp.. 
I have the 900u Monos and i compared extensively with 700 , 509, CL38 SE combo etc.
Simply 900u has nothing to do with the rest.
Luxman tubes best for triangle speakers.
They work well at low volume.
Regards