I have a large FLAC collection. I just made another folder and did an MP3 320 copy of my collection. I use it for my Camry and 4Runner. I got tired of dealing with issues and just went the most compatible format.
At MP3 320, you can't tell the difference from lossless after a clean conversion. Especially in a vehicle. You can tell the difference between the actual CD player and USB. What you're probably hearing is a difference in signal levels and OEM EQ for compression that is in newer music as far as I can tell. I have heard it. You either have to deal with CD's or accept the limitations along with the convenience of USB.
I use an IASCA cd to setup, calibrate, and EQ my system with a measurement mic. I then adjusted my method of conversion to better match the rest of the system. I use dBpoweramp and found certain settings that work well. I have a 900+ song collection of 80's music in one big album. Most of it is not compressed but some of the later stuff is. I despise constant volume adjustments more than using a touch of gain per track. When converting, I use the EBU R 128 (track gain) and set it at 0db. Audiophiles (Audiofools in most cases) will cringe at the notion. I have actually gone as high as +6db when experimenting in our new Camry. The JBL is terrible when playing non-compressed high dynamic range music.
At the end of the day I have an easy use USB drive that sounds great and matches well with other sources.
