well the Xonar STX (like my yamaha receiver) has TI Burr Brown DAC's (Digital Audio Converters. That is what converts the digital audio (data passed in 0's and 1's over a digital connection such as SPDIF (Toslink/Coax) or just decoding a mp3 file on your computer.
I use the receiver because I also have my HDTV powered by a video card in my rig and I use my PC to decode different audio formats from movie rips and pass them as multi channel PCM audio via HDMI to my receiver and 5.1 speakers. This allows me to pass all audio to one location and use the receiver to determine if I want it sent to the front headphone jack on my receiver or to the rear audio outs to my speakers. (This is mostly all handled by splitters and decoders that most people just refer to as "Codecs")
Sorta simple enough... Just keep in mind its sorta a gaming PC / HTPC hybrid which is why i run the receiver.
Now onto the headphones....
Differences in headphones come from dynamic range / Impedance (resistance a.k.a. Ohms) / etc...etc..etc...
I would go into the equations, but it is easier to just say that the higher the Ohms (impedance/resistance) on a pair of headphones, the more power is require to drive them to potential, which is where amp'ing comes in. The STX has 3 gain settings on the amp for different impedance headphones, which will allow you to drive more expensive headphones down the road.
Typically higher impedance headphones are much cleaner and when powered correctly REALLY shine. On the flip side, if you underpower them by using a stock sound card or a low end home theatre receiver, they are really going to underwhelm you and sound boring.
Low impedance headsets require far less power to drive them. And as a result, you get better volume and sounds, but at the cost of sound quality. (most common earbuds / gaming headsets fall into this category)
The auto sample rate non-sense is what you get when you pass digital (toslink/coax) through the sound card to a decent receiver. It will appear in the windows sound settings on most cards as something you can manually set. (44.1KHz, 48 KHz, 96 Khz, 192Khz) Most mp3 music and alot of FLAC is 44.1 KHz. Most agree that audio sound best when it is played back at the same sample rate it was recorded in. So when you use a output module that many audio/media players can use called WASAPI, it enables you to bypass the windows sound stack (where you would manually set it) and pass direct audio to your compatible receiver without resampling it. Most receivers with good components will grab whichever sample rate is being sent to it and just automatically adjust for the best quality sound.
If you need me to really clarify, I would say just PM me and I will try to send you some actually reading you can make sense of, but if I were to suggest anything, it would be...
Get the Essence STX. Set the sample rate to 44Khz in the Xonar Control Panel, Change the Amp to use the Front Panel of your tower and just plug your headphones in and go. If you ever buy higher quality headphones you can just increase the gain via the internal amp.
If you plan to get a home theatre or a 5.1 speaker set up in the future. I would instead use onboard audio, passed via a toslink cable to a decent yamaha receiver (such as an RX-V667) and run the headphones out of that... Keep in mind this solution really only makes sense if you want to integrate a TV/ 5.1/7.1 speakers / game consoles / cable boxes / etc...
Otherwise, most people buy specific 2ch headphone amplifiers and DACs and simple just use them for their headphones. This would be better researched on the HiFi boards here or over at head-fi.org
Be careful is all I can say... its easy to get sucked in Edited by rmp459 - 1/24/11 at 1:36pm