ARC Reference 2 MkII Preamp white noise levels

Tube preamps really do not like anywhere near that low of impedance. You might try asking your amp manufacturer if the impedance can be increased. Generally, there is an input resistor and you can simply substitute another value.
Most tube pre's are happiest when the impedance is around 50K or higher.
I really can't say for sure if this is responsible for the increase in the noise floor. Some tubes have a higher noise floor than others by a substantial amount. If the pre's tubes have been replaced, it's possible this could be an issue. Might check and see if you have replacements(different from the originals) if you purchased used.
If you purchased new---easy---call ARC. Or, call them anyway. They are really friendly people!

I'm not too certain about any plug in gadgets to correct the problem. I wouldn't doubt you could Google up some sort of pad to plug in between your pre & amp.

I assume you are using the balanced outputs on the ARC? The specs state that the output impedance halves at the single ended outputs. If you have some adaptors to go SE, it might be worth a try to see if that helps.

To confirm whether reducing preamp gain will help, you can do a quick test by using SE (RCA) output from Ref 2, if you are using balanced IC right now. The Ref 2 SE output (12db) has a lower gain then balanced (18db). However, if you have in-line attenuators, you can place it in between preamp and power amp to confirm it as well. It's working on my system (Pass X-600+ARC Ref 2 MK1) to reduce the noise floor (humm) quite a few. Hope this helps...

Well, 1K input Z, as soon asI saw that...this is the most likely problem. Too low for getting the best performance with ARC tubes.
Good luck,
JT

Actually the input is 10K Ohms, the balanced output is 440 Ohms for a 22x ratio...

I tried to track down the tech support agent at ARC but he was tied up. I'll try again Monday. Thanks all for your help.