I'm using a vintage pioneer stereo receiver. I don't have the model # at the moment.
The current iphones have good headphone outputs. They are definitely clean enough to use as a line out and feed an external amp. This generally works best with the volume turned all the way up on the iPhone. quick pic of my desktop streaming setup.
When double amping you should always set the source to max (or just under max) volume so make sure the second amp is getting something decent to work with (max SN ratio).
OK thanks... Yeah I am on a Comcast double play subscription now for internet and TV. Very happy comcast customer, I will look into that today for sure or my iPhone.
You might consider getting a FiiO L cable (or other brand), it will allow you to bypass the IPhones headphone amplifier and send a slightly cleaner analog audio signal from the iPhone's LOD port to the Pioneer receiver's RCA inputs.
I'm assuming you would need an adapter cable to connect the L cable to the RCA inputs on the Pioneer receiver.
6inch Premium 3.5mm Stereo Female to 2RCA Male 22AWG Cable (Gold Plated) - Black