Yes, you can change only one op-amp. The first(highest) op-amp on the left is responsible Stereo Line Output. One in red circle.
I have recently installed opa2107ap in my audiotrak prodigy and the sound is noticably better , so I recommend changing op-amps to everyone using this sound card. I bought mine on ebay for 12$ for two pieces.
I emailed support twice and have not received any replies.