You could take a look at the Emotiva BasX amplifiers though 6 channels is a bit of an odd number.
You could either go with a 7 channel or perhaps a 9 channel and do some bi-amping.
Emotiva do an affordable range called the BasX but they also have their XPA series.
We have both in the showroom if you wanted to see pics of them side by side.
The BasX A5 is a great choice if you're looking for a high quality five channel amplifier to power the 5 main channels in a surround sound system, or if you're looking for an easy way to upgrade the amps in your existing surround sound receiver. The BasX A5 is a five channel power amplifier that...
yorkshireav.co.uk
5 channel version above - they do a 7 channel though they're not on my website.
The XPA is a meaty one - I could configure a 6 channel for you (it's a modular system):
Emotiva XPA Gen3 is an audiophile power amplifier which can be configured with exactly the number and type of amplifier channels you need. Whichever configuration you select, your XPA Gen3 amplifier will deliver the same rare combination of excellent technical performance and superb sound...
yorkshireav.co.uk
Emotiva for me give superb quality / SNR / THD etc at reasonable costs. The prices like most things have gone up recently but one certainly to consider IMO.