The mx20vpr is a hot swappable 500 series Mic Pre from Danfield Audio. As one of the first members of the VPR Alliance their products work flawlessly with API's 500 series racks.
"The design of the mx20vpr is based upon our famous mx20 transformerless rack system, originally designed for classical tracking applications."
"It is designed for the engineer who wants absolute signal transparency when multi-tracking with quality studio microphones. The front layout is like all Danfield Audio products - very simple and user friendly.
The mx20vpr module is fully hot-swappable during operation. This is very useful in live recordings, where downtime is unwanted."
$629 at Alto Music.
Also take a look at their MX30-t Recording Channel.