Sorry for the delay, weekend chores call.
Anyway, no manufacturer I can find specifically states "using a power conditioner will void your warranty".
Some say "we haven't found a power conditioner made that meets our requirements", or "we recommend not using a power conditioner or ups system":
Krell specifically says to call before using one, Fischer and Rowland say similar things.
And then, at the rear of the manual under "warranty" it says "failure to follow directions (recommendations and/or instructions depending on the brand) in this manual will void the warranty", or as a bullet point of voided warranty circuimstances above.
So you can use one, and not void your warranty, as long as it doesn't have the recommendation not to use one, and the clause at the end saying "failure to follow..." yadda yadda.
Krell it specifically states you have to call first and DOES have the clause about installing outside recommendations in the book.
Emotiva has nothing about power conditioner use in their manual, but they recommend against it on their website. Their clause only voids warranties from unfollowed recommendations in their manual (specifically),not on their website.
Technically, if you stack your emo components without 2 powered fans, your warranty is void by the terms in the manual because you need 6" overhead clearance over the top of the case.
Manufacturers can find any number of loopholes to void your warranty at will, pretty much.
That clause at the end of most warranties ("failure to comply with the recommendations or instructions in this manual on installation, setup etc. of this unit will void the warranty"):
All it takes is that one clause, and a recommendation under setup or installation instuctions.
Or in Krells case, failure to call first.