Ahem - not an exactly Amiga-ish proposal, but why not run Linux/NetBSD/FreeBSD on a cheap piece of PeeCee hardware? Amix doesn't really feel very Amiga actually (does any U*ix?). It's a very interesting piece of software in its own right, but there's nothing cheap modern hardware can't do.
For the sake of 'modern OS hits ancient hardware' I've resurrected a PowerMac 9500 running Mac OS Tiger (a BSD derivate with a Mach kernel) - just slightly younger than a 4000 and rather cheap.
