The outputs of the deck to the HiFi amp ARE the speaker-level outputs. They just turn down the voltage a little when coded for HiFi. Otherwise there is no electrical difference. The ONLY possible problem is when you turn it up ALL THE WAY and you clip the inputs a bit. It already sounds heinous well before you get that far into the volume of the HU, so it's self-correcting. This is what works. (When the amp is turned on...)
musicar northwest portland or musicarnw.com
Web site migration complete, still repairing problems. Sorry!