I own the Furman Elite -15 PF i. I bought it primarily for surge protection and with the hope it would not make my system sound worse. I didn't necessarily expect it improve the sound of the system.
Listening to my system after installation I thought the Furman improved the sound. I wasn't certain whether it was just my imagination. Later that evening, my wife, who enjoys listening to music with me and has a good ear but is oblivious to my equipment - mentioned that she thought the system sounded better.
So I would recommend the Furman for surge protection. You may or may not notice an improvement, but I don't think plugging your amp into it would hurt the sound of your system. And by the way, it provides very good protection in my experience. Experienced a bad power surge and the Furman shut off before any harm came to my tube amp (tube amps can be especially vulnerable to power surges). Turned the Furman back on and everything was fine. Best purchase I ever made.

