Hi

Roon will read native FLAC files so you can just point it to where your files are, Sooloos as you say requires an import, up to you but I would cut out the middle man and go straight to Roon, there is a free trial so you could try before you buy.

Sell the MD600 as you do not need it even if you stay with Sooloos as the QNAPcan be store and core, it may be suitable as Roon core depending on the cpu spec?

Just my personal view, YMMV

Russ