[subsonic1050]

Big thank you to everyone, especially richidoo for your help on this. I had figured out that the RME was adding too much gain, but I never would have guessed I'd have to turn it down as far as needed without help!

[richidoo]

The output level on the RME is switchable from 19db to 1db on the XLR outputs and from 13db to -5db on the RCA outputs so go in the setup and turn it down before investing in new tubes.  All should be in the manual.  I suspect that the default setting from the factory is probably full output.

This is important to set correctly!
More info: https://www.forum.rme-audio.de/viewtopic.php?id=27767
This page says the pro level +4dB is set by default.
Change it to the -5dB setting intended for consumer equipment.