I have a cheap and generic 250 watt ATX Power supply that i hook to my car pc when I bring it in...just unplug the opus from everyplace and put the power supply in.
As far as power buttons, what do you want? Do you want one to control the opus, which has a shutdown and startup controller in it, or do you actually want an actual soft button to power your computer up and down manually with?
The opus doesn't really need a power button, it is switched by the ignition lead. I put a switch in my cigarette lighter that i got out of an old PC case (old old...before they were momentary...meaning that when you hit it it switches between on and off, like a light switch). As a matter of fact, you could use a light switch if it were hidden...they're only like 30 cents.
If you want a soft power button...well...on an M1000 board you can turn it on and off by jumping a paperclip accross pins 6 and 8, I believe. So anything that connects those pins for a second will work. What I would do is find an old crappy computer at a garage sale, and take the wiring 'harness' out of it...this will include the PC case speaker, the HD activity LED, the power LED, the reset switch, and the power switch, with appropriate little slip-on connectors, and use that for yours. If you look on page 2-11 of your Epia manual, it has a pinout for the front panel connector...just hook stuff up where it says. For example...put the speaker connector between pins 7 and 13, put the HD LED+ on 2 and LED minus on 4...etc etc. Just try it, it will be obvious.
If this doesn't make sense, reply or PM me for more details