Anyone using ARC pre-amp with Machintosh amps?

ARC recommends amps with at least 20k impedence for their pre-amps
Macs are 20k.
general rule: input Z(impedance) of the load should be at least 10 times the output Z of the source.
2k-ohms seems like a relatively high output Z but if this is a tube ARC pre it could be that high. Still from a spec perspective seems like this arrangement should work satisfactorily for you.
What Bob said.

Only concerns I could see would be using long ICs with high capacitance.
A friend is using the ARC Ref. 3 with Mac 1201 monoblocks and the sound is great. He has had this setup with no issues for almost two years.
I have used my Ref 3 with a Mc402 often and it sounds great. The output impedance is quite low for a tube amp at 600 ohms.
Sounds Great to me ! I'm using a ARC SP 15 Tube Pre with a Mac 2500 Amp.