No, to my ears the 509X is definitely not as good as a ~$6000 used dedicated line stage. I used it from time to time to drive my Luxman M800a power amp. It sounded pretty good and quite neutral, but was outclassed by my PS BHK and Allnic L3000 preamps.
If you're buying it for dual purpose--to have 2 amps you can switch between--it's a fine choice with lots of flexibility.