Hi, bought a hk avr 520 on ebay for a grat price used. Doesn't have ANY jumpers between preamp and main in. I don't get any sound from any of the speakers unless I plug a source into the main-in terminals, but then I get no volume control (but the speakers definitely work then). Do I have to have jumpers between the pre out, and main in for normal operations or is there something else wrong with the receiver? The manual talks about them once as if they're default. Where can I get some or how can I make cheap, but good DIY jumpers. I don't want to spend $40 for a set of two on the internet. Any advice would do. Thanks in advance.