My klipsch forte 4 just arrived last week. From 1 hour to 10 hours of listening, it is not bright for me. It has about the same "brightness" level comparing to my other system (Luxman 595A, JBL4349, mixture of furutech and inakustic power cables, speaker cables and interconnects, etc). For the Forte, I have Fluxion intergrated 300B pushpull with black treasure Shuguang, Sylvania tubes. I do not think the Forte speakers are bright. As Carlsbad mentioned, check out your cables. I think having TWL speaker cables help in my case (I recommend TWL to reduce "brightness" in this case for speakers and power cables). 300B definitely would help. The rest of cables are the cheap $1 cables from my TV's (run out of cables).
I hope this helps.
PS: 8W is not enough power to drive the Forte as I noticed. My room is 10x12. 15W is perfect for most listening cases. If you look for a tube amp, try at least 15W to get it covered. I have heard 1W-2W recommended by other folks. This is true for low level listening.