6 Channel Homebuilt amp

Welcome to the world of DIY audio. You'll likely never go back to commercial products. There are lots of amp options. What is your skill level? Any electronics or metalworking experience? If one of those six channels is for your subwoofer, you might want to consider significantly more power for it.

There are a variety of chip amp kits available from several vendors. Until you bridge LM3886s you won't get to 80W, but you really won't notice the difference between 50 and 80W.

Rod Elliot has some good projects and provides good support. P3A is a nice amp 60-80W Power Amplifier, as is P101 although the output devices are a bit more expensive and harder to source.

Check the group buys section for some other PCB options.

For a less intense building experience, check out Aspen Amplifiers Hugh sells some very nice modules ready to bolt into your enclosure and hook up to your power transformer as well as modules for which you will need to supply a heat sink and power supply.
I don't know that lots of people have built Apex amps like the others I mentioned, but the designs seem sound. Go for it, if you think it will suit. Does he sell boards? Build the smaller amps first and get the hang of it. Larger amps have more potential to make a mess if you've goofed something up.
my 2c: You'll need to give some thought to the power supply if you go with a ClassAB amp - 6 channels at 80W is a fair demand which leads to large transformers and slow-start circuitry for powering it up.

If you want to learn about DIY audio then an HT amp gives you plenty of scope to do that. If you want to get a 6 channel amp up and running as soon as possible and still build it yourself then the chip amp suggestion is an excellent one.

I decided my HT amp would be fully home grown, my own power supply and amplifier design. It took at least a year before it was in service.