I have found this valuable information.
According to Skyward @ gamezone24:
http://www.gamezone24.net/forums/showthread.php?28773-Audio-The-OP-Amps-thread!-(for-advanced-users)
"As I am using an Asus Xonar Essence sound card, i'm gonna take it as example: old Asus Essence devices used crappy OP amps, so in order to improve the sound you will have to replace all of these.
Their latest product brings two
Muses 8920 and one
Muses 8820. In the package they include 3 exchangable op amps: x2
LME 49720 and x1
Muses 8820. All you have to do is to take off the
Muses 8820 from the Buffer and place a
LME 49720 instead.
Muses 8820: The dark beast! Commercially speaking it sounds great because there's the name Muses on it, and they're well known for their Muses 01 which are certainly the most renowned op amps actually on the market. However, they are very crappy and you must take these off and use better ones!
Muses 8920: The best one, why? because it's specs are very close from the Muses 01 and it costs only 17€ instead of 75! It's pratically the same as the LME 49720 but the sound rendering is more like what tube amplifiers provides (J-FET technology) so that makes it a bit better than the LME 49720.
LME 49720: Well as I explained above, it's more like the same as the Muses 8920, slightly less good since it uses bi-polar technology. But it remains a sure value.
Muses 02: Don't get fooled! Its name would make you believe it's right behind the Muses 01, but that's not the case! That thing is not worth better than the crappy Muses 8820. And it's 50€ one!
Muses 01: The reference, the legend. Renowned by every audiophile, those amps belongs to the best actually comercialized on the market. It's 75+€ one.
Beware! Yes, some Chinese manufacturers are selling false copies! So watch out if you see, on ebay especially, resellers selling those for 15 bucks only.
There are a lot more models but I don't know them all. Those I listed above belongs to the biggest references and are probably the most used on all "audiophile" devices and materials. There are also some that costs a lot more money, but remember that in the audiophile world, the price doesn't always justify the quality!"
"For anyone using that kind of sound card with 3 double OP amps, i'd recommand to use:
- x3 Muses 8920
- x2 Muses 8920 (I/V) and x1 LME49720 (Buffer)
- x3 LME49720
- x2 LME49720 (I/V) and x1 Muses 8920 (Buffer)
- x3 Muses 01 (if you got the money)
- Any other OP Amps you think would be better than those listed above"
What do you think?