Hissing sound coming from tweeters

I don't want to get rid of the speakers or the pre-amp. If I have to get rid of the Emotivas eventually it wont be a big deal. I think I got them for $279 each, which is minimal compared to the speakers and the pre-amp. I like having some headroom that the more powerful amps offer. Unfortunately I went cheap and bought the Emotivas. I couldn't find anything that packed 200 wpc that matched the same price/quality point as the Emotivas. When I bought all my equipment I wasn't thinking about s/n ratios or anything like that. Shows how little I know about building a quality system.

89db snr @1 watt isn't high enough?

I'd experiment with cable placement / orientation before changes which cost $$$.
See if raising speaker cables off the floor or getting them away from the interconnects makes any change.....

SS ammplifiers and sometimes preamplifiers can have a hi noise floor most never hear it because designers thought only low or average efficiency loudspeakers would be used. And most do such. But if using horns on SS it can be hard to find a low noise SS design. I do know NAD newer bee amplifiers are horn friendly and affordable. I design loudspeakers and trust me SS amplifiers can have more noise on horns than tube amplifiers.

Have you tried cheater plugs on the amps? Works sometimes.

The amps have a 5 year transferable warranty. Maybe you can contact Emotiva and see if they will ship you another one to try - just in case it is something wrong with your amps. Or they may have suggestions to try. I have been reading the Emotiva board and a small number of people do seem to have hiss/hum problems - not common but certainly some reports of issues.