Another thing to consider are insert nuts, Basically, you drill a hole in the wood, use an allen wrench to screw the insert nut into the wood, then, you can screw a regular machine bolt into the insert nut.
You'd need A LOT of them to put together a whole cab using angle brackets but it can be done.
Another possibility, separate the top and bottom. Would you be able to get just the top part and then the bottom part down the stairs? If so, you could saw the cab in half horizontally, then fashion a mating plate for each side to mate the two halves back up with screws once they're in place. I did that once with an entertainment unit that wouldn't fit around some funky stairs I had in a house I used to own.