The 500 B I ordered from eBay arrived today. The unit does not have a cabinet. Two questions: 1. Should I elevate the receiver using shims so that some air can circulate under the chassis? Without a cabinet the th bottom of the chassis comes into direct contact with a shelf. 2. Did Fisher manufacture metal cabinets for the 500 B? I only see wooden cabinets on eBay. Are there any worthwhile aftermarket cabinets available anywhere?