Picking an amplifier

Hey there, I totally understand wanting to wait and do things one at a time.

It appears that the card holds its own in most catagories, but comes up short in catagories such as soundstage.

You might be reading about the card's analog output.  I am guessing this is due to the op amps used (STX II uses the MUSES op amps, the original ST/STX used the LM4562 op amps).  The soundstage would be improved by upgrading them to something like OPA2211 or AD797, but that's not what you would be using the card for.  You would only use the card for digital COAX output.  As far as I know, this is the best solution that supports Windows 10.  There are other cards, but they are older and limited to Windows 7 (such as M-Audio) or they might not have a proper COAX (using a 1/8" plug for spdif), or they are insanely expensive like the RME Audio card at $1,000.

Secondarily will be Bluray formats - still getting up to speed on how who is releasing what music formats on bluray.

No problem.  As I said, you would need an HDMI interface for the bluray audio formats.  HDMI is the only licensed interface that will support Dolby TrueHD and DTS-HD MA formats.  You could do this by getting a video card with HDMI output.  I read a little that VLC will support audio through the HDMI output.  Other players, such as JRiver or PowerDVD, should support it to.

If you used COAX or optical output, the player software would have to down-convert the Dolby TrueHD / DTS-HD MA to the older compressed Dolby Digital or DTS formats before sending the bitstream data out.  COAX will still support 2-channel PCM audio up to 24/192.

Wow, that Asus Xonar HDAV looks like a good find!  The “Deluxe” version has good power supply sections and looks to have good TCXO clocks.  However, it appears that Asus only developed drivers up to Windows 8 for this.  (Windows 8.1 and 10 are not supported).  The card was discontinued a while ago.  If you are running Windows 10, the ST / STX / STX II are still supported with new drivers.

I read that article “Why Audio formats above 16/44.1 don’t matter”.  This has been a controversial subject in the industry.  I will say that several years ago I did some testing.  I took a 16/44.1 version of a song (CD audio) and compared it with a 24/48 version of the same song from the same album through my Krell HTS 7.1 processor.  I did definitely hear a difference.  The CD version with lower bit depth / bit rate sounded a bit messier.  The 24/48 had a cleaner and more solid sound and the resolution of individual instruments was definitely better.  I will say that it needs equipment with very high resolution.  Otherwise, you probably will not notice any differences.

I also have done some testing recently comparing both 2-chanel PCM audio and 5.1 DD/DTS through different transfer mechanisms. 

When playing a movie, the Dolby Digital / DTS is an encoded bitstream that is sent to the processor through a digital cable such as COAX, optical or HDMI.  The processor will then decode the data and split the data into individual PCM channels (such as 5.1 channels).  It will then clock the individual PCM words at the proper sampling rate (such as 48khz) and then sends it to the DAC chip.  So, ultimately, there isn’t much difference between COAX/optical and HDMI for this transfer.  It’s really just data at this point.  However, if you want to be able to decode and play the bluray hi-res audio formats (Dolby TrueHD / DTS-HD MA) you must do this through an HDMI connection (licensing restricts any player/software from transmitting this through old spdif coax/optical).  If you do use a COAX/optical, the player will automatically down-convert to old compressed DD/DTS formats.  There is a difference in sound quality here.  The compressed stuff sounds very rough in comparison.  The hi-res TrueHD/DTS-MA will have a smoother and more realistic sound.

When playing 2-channel PCM audio, such as CD or 24/96 hi-res, the player/transport will take the raw PCM data and clock it at the proper sampling rate (such as 44.1 / 48 / 96).  It will then send this “clocked” data over the digital cable.  The COAX/optical works well here.  However, this is where HDMI cable will be severely compromised.  The HDMI transfer is not raw bitstream data.  It is done in data packet format, which means these “clocked” PCM frames will be spread across and combined into multiple HDMI packets.  This means the “clocking” of the audio is already compromised when the processer/DAC tries to “un-wrap” these HDMI packets and send it to the DAC chip.  So, as a comparison:

2 channel 24/96 through digital COAX.  One weird behavior of the Krell processors is that it down-converts anything coming in from digital spdif to 48khz.  I don’t know if other processors do this, but this has been normal Krell behavior for a long time (they must think it is a licensing restriction).  Even though my 24/96 songs are down-converted to 24/48, the sound is still amazingly excellent.  The sound from COAX just sounds so much more “natural” and has excellent dynamics and excitement.  I love listening through this mode.  SIDE NOTE: I have tested my Oppo player connected to a DAC through digital COAX and the DAC is receiving and playing 24/96 and 24/192 just fine.  It’s the Krell that is down-converting to 48Khz through COAX/optical.

2 channel 24/96 through HDMI (i2s) interface.  On my Krell, this was the only way to get the Krell to play true 24/96 or 24/192 at those proper sampling rates.  I can hear that the resolution of the audio is better than 48khz through normal COAX.  However, the sound is more “controlled” or “flat” sounding.  There is no real dynamics or excitement to the sound.  Also, the upper mids are “shouty” and have “blare” which can sound a little painful at times.

So, to sum it up:

Digital COAX/optical – compromised bluray audio, but excellent 2-channel audio

HDMI – excellent bluray audio, but compromised 2-channel audio