I'm interested in responses to this as well because I am looking at getting an HD Pro rack unit. Does anybody use one in their studio? I would go from the rack unit to a VOX ac4tv (which would be miked).

I have an Avid Eleven rack. No complaints. It actually FEELS like an amp. In some instances it sounds very much like one by itself. Since I have a VHT Pittbull 45 I use the Eleven rack for bed tracks and the occasional effects channel through an amp.

This probably does not help the OP, but Fabfilters just came out with a multiband distortion/saturation plugin. It does lots more that just simulate amps. Here is the demo featuring the dulcet tones of Dan Worrall. The feature set looks great. I haven't been using this type of tool that much lately, but I'm definitely going to give it a spin soon. Love the Fabfilter "Pro-LCGQ" suite.

Any thoughts on the Korg Pandora PX5D?