Just wanted to relay what my experience has been with opamps. I am using Sennheiser HD650 headphones straight thru the xonar stx. I have the rca outputs going to a Harmon-Kardon avr 510,connected to Electrovoice Sentry V's. Sounds real nice thru either but we all want a little more. If I use the headphones thru the receiver the sound is not quite as good as what I hear through the headphone out on the xonar itself. So most of my listening has been thru the head out jack. Reading here on the opamps, I finally decided to give it a go. I bought 3LME49720NA dual opamps and just installed no problem. The difference for me was clear. The soundstage seemed a bit larger, but the sound seemed a bit thin. The bass was well defined as was the treble and midrange, but just a little less life to it. I listened to hd flac, mp3, wav all were the same. On occasion would hear a little sibiance that never showed up with the stock opamps. Listened to all kinds of music for a few hours, and decided to go back to stock opamps, but before I did I put on the avr, and tried the sound on it. Wow, what a difference in the sound on the line out, even the wife had to come back and listened a bit to the difference. So naturally I figured I better try the headphone out on the avr, again, big difference from the stock opamps. Now using the Senns thru the headphone jack on the receiver, I have what I was looking for. More openness better and more detailed bass, treble, headphones sounded so realistic I spent another two hours going through as much varied material as I had, just to make sure it was good to go on all types of music, and it is. Best twenty dollars I ever spent, now I am a happier camper than before. NOw I have to decide if I want to reinstall the opamps for the headphone section or just use the avr. The detail on the avr both speakers and headphone is beautiful, I guess if it "ain't broke don't fix it" is what I am doing. Hope this helped someone that is on the fence to try a little opamp swapping. Of course your milage may vary. All the best.