a follow up:
 
as to my buddy's recording session using some of my gear, and adding IR's into the mix:
 
total success.
 
they had done previous sessions, using actual sm57 on vox AC30's, good sessions, but they repeated the tracking of the same songs using IR versions of the real thing (sm57 on vox ac30 with celestion blues) and said the sound quality was night and day.
 
interesting.
 
that was done using my weber Mass Lite's line level out to control the input level, using the attenuator as the only load,  monitoring thru the mixdown monitors using the plug and IR, got their best results to date.
and that was on the first try!