What is the BEST way to get audio (line in) into my new iMac 21.5? They removed the mini-jack audio input. Argh!

I record audio professionally. I recently sold my 27" iMac 2011 model with the the line IN mini-jack.

I have bought a USB adapter, which makes my microphone sound distant, tinny. It *****. I have professional audio, microphone, Peavy mixing board and professional audio recording / mixing software.

I need a real solution for this. Help. What can anyone else out there recommend for me?