If you're considering a built-in cabinet I'd suggest locating the fan in the attic to get the fan noise as far away from the equipment, and listening position, as possible. It can vent either directly to the attic or be ducted to the outside like a clothes dryer with a one-way flap. Although, if the latter you might get cold air blowback in cold weather even with the flap. Best choice of fans would be a squirrel-cage type, like the fan on home forced air furnaces; but smaller. The fan control can be located in the listening room for convenience. That type of fan is more efficient than a rotary blade fan and you can move a good quantity of air with a relatively small fan. The fan's CFM shoud guide you as to size.
Slatted wood shelving - perhaps maple for its resonance-draining properties - would facilitate air movement although these may need to be custom made.
Slatted wood shelving - perhaps maple for its resonance-draining properties - would facilitate air movement although these may need to be custom made.