Amps and Quatros

Congrats on the Calypso, it is a fine preamp. Tube preamps with SS amps are a popular combination. I would check out the McCormack 500 that you've previously mentioned, as well as the Ayre V-1xe or MX-R mono's that Theo mentioned.
You may also want to give the Pass X-350.5 a listen.

If you would consider a single ended amp, you may enjoy the music through a Conrad Johnson Premier 350.

Happy hunting,
John

All the Pass Labs .5 series sound close. Only the bass is slightly different(as well as power) but, sonically they are very close. Since your Quatros have a bass amp powering anything under 100Hz then just about any Pass will do.If I were to go solid state with your options that you've listed I would go Pass 100%. Ayre is too light,DNA 500 is too soft and muddy in the bass, so is the CJ Premier 350A,etc. The Pass is the real deal.If I could not go for the Pass the next would be a Sim Audio W-5 LE. The Pass has just the right amount of everything whereas the Sim is just a touch dryer but it has tight bass and upper extension that the others don't have. If I were to go tubes( I know you didn't mention this one) I'd go with a Music Reference. Either a RM 9 or RM 200. If the money isn't an issue then I would recommend an ARC VT 100 MK III or a Reference 110.

Thank you for your comments. Does anyone have an update on the tube problems with the calypso?

What tube problems with the Calypso??