So I owned MXR's for about 5 years and recently sold them vs upgrading to MXR-20's. While the 20's while technical better, they were missing that magic I loved about my MXR's.
I ran 2 preamps with the MXR's. A Nagra PLL and now a Koda K10. The Ayre KXR is also a very good preamp...I got to AB the Nagra and the Ayre in my home. The Nagra added a touch of sweetness to the notes, the KXR was a lil bit more quiet and more resolute. The current Nagra preamps (Jazz and Classic Pre I suspect are just killer good-I'll get to demo a Nagra Classic preamp hopefully over the holidays)
The Koda K10 is just a wonderful piece. Beautiful colors, textures, just totally get's out of the way. I've now had it for ~4 years.
Good luck !