Why does your print server need to go into sleep mode instead of just shutting down and booting back up for print jobs? Booting it up remotely can be done a few different ways, IIRC. Having it shut itself and the printe down after a set period of inactivity would be duck soup, IIRC. Back in the day I used a PowerKey Remote(?) to boot up the Tandy 1000SX w/JT-FAX Card and the printer whenever a FAX came in wqhen I wasn't in the shop.

The Macs don't shut down mp because they're expecting an Energy Star m to be p'd. It's a simple relay setup in the PSU to implement mp, no intelligence is involved to detect anything at all.