hospital grade or commercial grade receptacles ?

Almost all hospital grades (with the exception of the 20 amp Hubbell hospital grade sold by Albert Porter and Take Five Audio) have nickel plated contacts, which I would suggest you avoid. In that respect, you are best to stick with a spec grade receptacle. My personal preference, not having heard the non-plated Hubbell above, would be either a Hubbell 5262 or 5362. I have doubts as to whether I would be able to differentiate between those receptacles.

Different receptacles have very different sonic signatures, and cryo will make a significant difference IMO.

Contrary to the respondent a couple posts above, power cords and receptacles do make a difference. If you can, I would chase down on A'gon some of the "Porter Ports" that member Albert Porter was kind enough to make available. I have one and it did make a difference. Reasonably priced too.

Good luck,

If power receptacles make a difference (and I doubt it) you would be better off using ones designed for high current high voltage applications, like you stove or clothes dryer. These have contacts with much greater contact area, and some have a twist-to-lock feature that provides a wiping action for the contacts.

Another pointless battle between those who hear differences and those who don't- which has to depend, I have come to believe, not on differences of hearing but on the resolution and nature of the equipment used. In my case, Wattgates and FIM outlets sound different from one another in easily described ways, and better than stock, by far. No competition, no subtle differences, night and day stuff. In my experience, too, although not with outlets, I don't like the sound of cryo'd components: they tend, consistently, to sound more forward, with less air around images, than stock versions of the same. It's a matter of taste.

Check out PS Audio outlets, they are the best I have seen.