all IR's require some form of power amp by their very nature. Imagine you are taking a photograph....if you were in the dark, it wouldn't matter who or what is in the photo ...or what camera or lense is used....Ok maybe not the best analogy but...
So a solid state power amp would be the most neutral, analogous to say natural daylight and have the least effect on your sound, other than the desired cabinet and microphone.
An IR is a closed loop that contains the attributes and artifacts of the aggregate of cables, analog digital and digital analog conversions, mic pre (and settings), the microphone, the cabinet, the amplifier used for the test signal and the room. Of all these parameters, one could (arguably) say that the cabinet, microphone and its placement are by far the dominant factors. As IR's for speaker emulation gain popularity, many creators of these libraries have expanded the information describing the details of their processes. In the end, the best result is what sounds good to you (in my opinion)
Andy