Since you are getting no responses, I will give you a couple to try out, that are found relatively often on Audiogon.
Either the Levinson 33's or the 33H's.
Both have been very well reviewed.
They don't have the power of the Pass X600's, but they certainly have the credentials as being sonically good as a solid state amp can be. (Do you need that much power by the way? What are you driving?)
Also, VTL makes some pretty nice tube amps that have similar power to the Pass X600's. The Reference 750's are what Albert Porter is now using to good effect with his Soundlabs, and my friend is using the MB-450's with his Eidolons. (The MB-450's sound great, and will not clip, even when driving his speakers to very loud listening levels with very large symphonic pieces of music!)
Just a couple of possibilities.
Good Luck in your search!
Either the Levinson 33's or the 33H's.
Both have been very well reviewed.
They don't have the power of the Pass X600's, but they certainly have the credentials as being sonically good as a solid state amp can be. (Do you need that much power by the way? What are you driving?)
Also, VTL makes some pretty nice tube amps that have similar power to the Pass X600's. The Reference 750's are what Albert Porter is now using to good effect with his Soundlabs, and my friend is using the MB-450's with his Eidolons. (The MB-450's sound great, and will not clip, even when driving his speakers to very loud listening levels with very large symphonic pieces of music!)
Just a couple of possibilities.
Good Luck in your search!