Which pre amp s suites my YBA 1 Alpha hc amp?

Why not the obvious and a YBA preamp?

Its own, CAT ultimate, placette active, EAR 864, Copland (older models).. to name a few. There are many others. It's a somewhat difficult load (choose a pre that matches well with a 25-30kOhm load) -- but other than that, it's the sound that matters. To state the obvious: try out a few pre's starting with its own.

A YBA pre amp with your YBA 1 amp would be a match made in heaven. If finances permit I would try to get a YBA 1 pre amp or higher. However other YBA models would match as well.