Hi Rjlitho,
Well-designed separate solid-state power amps like the ADA 1500 do not have to be "set" to a specified impedance such as 4 ohm or 8 ohms. Unlike many receivers these days, they do not have current-limiting impedance switches, which severely cut the receiver's power output to prevent overheating driving a 4-ohm load. Solid-state power amps have sufficient heat-sinking and cooling so they can easily drive 4-ohm loads without shutting down or limiting their power output.
So just connect your VP180 and enjoy its high-quality sound without worrying about its 4-ohm impedance.
Regards,
Alan
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