I’m using a 306 to drive a Quad ESL 63 - there are passive subs driven by another amp. I don’t use a preamp at the moment, I control volume digitally.

I’m tempted, just out of curiosity, to try a 909. There’s one for sale on eBay which I can return if I don’t like it.

Is it a waste of time? How will it change things?

Are there any pitfalls to look for when buying the 909? Are all 909s the same? Does recent servicing make a difference to how they sound?