@erik_squires
There is a bit more to that than that. I've had both. Recently sold the 505 and replaced it with 507. The preamp section of the 507uX is better as is the output stage. How much better? Depends on the speaker. Not much of a difference on Aerial 5Ts. Much better bass grip and bass to lower midrange integration on Aerial 7Ts. 507 doubles down into 4ohms. 505 doesn't.
There is a bit more to that than that. I've had both. Recently sold the 505 and replaced it with 507. The preamp section of the 507uX is better as is the output stage. How much better? Depends on the speaker. Not much of a difference on Aerial 5Ts. Much better bass grip and bass to lower midrange integration on Aerial 7Ts. 507 doubles down into 4ohms. 505 doesn't.