For the last 16 years I've used a Sparkmatic modulator, which came out a generation ago to let you input your portable CD player(Mounted on a flexible arm), as far as I know the Company is defunct. The sound quality is near perfect.

Recently, I purchased a Nikkai modulator for my other car, it's squelchy and lacking in tone.

My point being that it is possible to have one that works effectively. However, overall an input/adaptor to the HU is a better solution.