What's the best pre-amp to use with the Acurus

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...a tube preamp with a low output impedance. Maybe a Quicksilver or something.

After having used an RL10 with the one I used to own I would recommend a tube preamp.

I had an A80 paired briefly w/an Aud Illusion M3, and it produced a transparent soundstage that blew my mind...truly three dimensional and DEEEEP. However, it was a bit too bright in the upper end, which was the Acurus. You might try a CJ or Cary. These are a little warmer and would pair well w/the more forward upper end.

I really can't recall, but I seem to remember the Acurus as having a rather a rather low input impedance. Finding a compatible tube pre might be a challenge.
I remember the Acurus amp as having bass capabilities way beyond it's price point, unfortunately I also remember the upper end being dry and chalky.
If you can find a tube pre that has an appropriate output impedance, I think that might be the way to go.

A tube preamp sounds amazing with the otherwise slightly clinical sound of the Acurus.

I had an Acurus A250 for years...a great amp even though I used it with a mediocre Adcom preamp. I did borrow an Acurus L10 preamp (from the dealer) for a while and it sounded amazing although I couldn't afford it for some reason. I think the Acurus preamps do look cool though...and they're inexpensive.