LUXMAN L509X VS M700/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 

Deltas don't do well with solid state. I had them with tube amplification after been unable to match them with SS for months.
They are moderate efficient speakers buy they need Current to control the multiple drivers design. Stay away from SS if you keep deltas.
Best,

If the OP had started with a Luman SS Pre and wanted to go something to soften the highs, I'd completely agree, go tubes.
However, the OP is starting with an Oppo HA-1 which, IMHO, is awful. If he can listen to that, then going to the Luxman will be a huge improvement across the board.

He _should_ listen.

Also, yeah, I have problems with the Triangle horn tweets, but I wonder now how much of that is placement. Don't toe those in, and make sure you have lots of high frequency absorbers around the room, especially between and behind the speakers, including the floor.