My 1st Tube Equipment Experience

I was researching the viability of using an RCA to XLR cable, with RCA on the Herron and XLR on the M22. Might that help, or is it a bad idea.

It won't make any difference. What might help though is to make sure you have a jumper installed in the M22 between pins 1 and 3 of the XLR when using the RCA input. This will prevent pin 3 from picking up noise.

The RCA connection is single ended and that won't change if the other end of the cable has an XLR connector on it.

@atmasphere. Thanks for insight and advice.  

I've finally found my sweet spot with the Herron and NAD settings.  The Herron gain is set to low; the NAD M22 v2 gain is set to mid.  Now I understand why many here have recommended a tube preamp and SS poweramp.  I'm quite happy with the Herron/NAD combination.

I also re-positioned my speakers.  I have a small 11x12 listening room.  I placed the Tannoy's 36" from the back and side walls, and toed them in about 3/4 of an inch.  My two listening chars are a little more than equidistant between the speakers.  No more glare and I can listen for hours with no music fatigue.  I'm finally enjoying digital music as much as analog. 

Now I'm wondering what a better DAC would do.  I have a Mytek Liberty, which sounds pretty good with my current setup.  My planning budget is ~ $2.5K.  Suggestions anyone?

My preference is a tubed NOS R2R dac, very analog sounding. 
I have been very pleased with my Audio Mirror Tubadour III. Sound wise it comes pretty darn close to my analog - VPI, dynavector, Herron audio vtph-2a. 

Now I'm wondering what a better DAC would do.

:)