The $20K Soulution Audio 330 Integrated Amp is a Bargain ?

I've heard plenty of good things about the 509X. Only you can say whether it would suit your needs and the needs of the rest of your system and budget

I would think the Analog Domain plays more in the realms of a C/M900u combination. The following review offers a good perspective

https://www.hifi-advice.com/blog/review/analog-reviews/amplifier-reviews/analog-domain-m75d-and-m75p/

I've not heard the 330 so couldn't say how that'd compare

With quite a few $20k+ integrated amps around vying for attention there are great options for those wanting to de-clutter their system without compromising sound.

I went for an Analog Domain integrated and it's a remarkable thing. I've not heard the 330 but I have some experience of the 725/711 combo. The AD gives little if anything away and I like the big Solutions. Worth noting Soulution needlessly get a bad rap. I've heard that same combo sound awful through incredible, all down to set up and system matching. 

For the poster looking for speakers for his 330, best I've heard with Soulution were Verity Parsifal, a brand worth investigating