I also have an ATI AT 2007 power amp and it also takes around 15 to 30 second to power up. This is there soft start circuitry in action as to not blow circuit breakers on power up. It also keeps connected speakers from "thumping" on turn on. I know of other folks running 3 ATI amps on the same circuit and they can all power up without popping his circuit. I actually like this idea as my old B&K ref 2007 amp would "pop " my speakers on startup and shutdown.
Yamaha CX-A5000, ATI AT 2007 Amp (7X200W), ATI AT 2004 Amp (4X200W)Klipsch RF 63's - Main, RB 61's - Front heights, RC-62 - Center, RS-62's - Surround, RS-52's - Rear Surround, 2 Rythmik DS-1510 DIY Subwoofers (With PEQ600XLR3 Amp) each connected with Antimode 8033S-II, Oppo BDP-95, MMF-7.1, Project Phono Box RS, XBox 360, XBox One