The Sjostrom Audio web page is showing the bare PCB and built units so I guess he's meaning he doesn't sell them boxed and ready to use?

6 amps (just shy of 1.5kw at 240 volts) should manage most kit I have, the bigger DSPs I'd want to check and think about 1 per speaker? Despite my noisy mains I've not been bothered by buzzing PS in my DSPs. I did have my M80 quite noisy once though!

The Altaudio unit I linked does come as a built unit boxed to use and is a very similar design, the HFWW link you posted suggests they have a good following too.

Regards

Richard