looking for good amp 5channel or 7channel

any suggestion... I have a dennon avr 4800..trying to find a very good amp or can I just upgrade to new 5800 instead..
also guys.. what do you think about the new sunfire sig.series...
Might I suggest ATI? I am a custom installer, and have had great success installing them in situations such as yours. They make two five channel amps and one six channel amp. Each channel is rated to either 150 or 250 per channel. The amps can also be bridged for even higher output, although I can't see a sitation where this would be necessary. If you don;t have a local dealer let me know, because I can give you a really good price on there great amps. Some have likened them to a Krell amp at a real world price. Check out their website at www.ati-amp.com.
BAT VK 6200 can be configured in five channel. I run one with four channels, biamping to two channel, and it's awesome. In a five channel mode, the 6200 has separate, huge output transformers for each channel, and will smoke most others, IMHO.
Limiting the scope to your original questions, I think it really depends on what you want out of your system. I went from using the power amp from a Denon 3030 to using a Sunfire Cinema Grand and the difference wasn't huge with low quality input, things like VCR tapes. It was nicer, and it was there, but overall the change was somewhat disappointing. CDs improved nicely, but I wasn't stunned by their quality. On the other hand, high quality input like DVD sound tracks took a huge leap, and went to theater quality. I don't have a turn table hooked up, but I would imagine it would also be tremendously improved. The sound from a good movie soundtrack still makes me sit up and take notice, just because of how good it is. So, I would suggest that the decision depends on what you want to play. I would also factor in whether or not you will be upgrading the rest of your system to take advantage of the quality of the amplifier. Feeding a Sunfire from a Denon will never really take full advantage of the Sunfire.

Since I play a lot of DVDs (I work for Netflix.com) I would never go back. On the other hand, if I was planning on keepintg the Denon front end and didn't play very many DVDs, I would probably stick to the Denon power amp.

I like the Sunfire Cinema but I haven't tried the Signature. Generally, I think they sound pretty close to each other. Do you really need that much power?
If your objective is to have a multi-channel that also does a good-to-excellent job with pure audio reproduction, then you should add the Bryston 9B-ST to your short list (125 wpc x 5). This unit is "Class A" rated in Stereophile, and has gotten rave reviews from many other audio / HT reviewers. To see the reviews of the 9B-ST, go to Bryston's Web site at: www.bryston.ca
The Bryston is another great amp, which comes with a twenty year warranty. We could probably be more helpful if you listed your system configuration, particularly your speakers, since synergy is everything.

Also, what are you planning to use the system for, mostly home theater or mostly music or a mix?