The Asus Essence STX II comes with multiple Op-amps. 

Default heeft de Asus Essence STX II : 2x Muses8920 in I/V en 1x Muses8820 in Buffer

I did read a bit and people prefer the LME's over the Muses. Gives more and tighter bass. So I will change the 2x Muse8920 to 2x LME49720 as I/V
Now someone on a forum mentioned to put 1x Muse8920 as buffer instead of the Muses8820. Yet I could find only 1-topic post about this
Yet I read somewhere that the Muse8920 is a JFET. Can it be placed as buffer?


In package:
1 Op-Amp change equipment
2. 2x LME49720's and a spare MUSES 8820 

I know that some people prefer the Muses01 and 02. They are 50 dollars each. Yet I live in the Netherlands and I cannot find a Europe-seller. Although 150 dollars now is a bit to much. Bought also a 980ti so ;P

The STX II's headphone output only uses the two I/V slots.
The STX II's line-out (speaker output?) uses both the I/V and buffer op-amps.
 
All three op-amps slots on the STX II are DIP-8.
All three op-amps that come stock with the STX II are DIP-8
So yes, any of the stock op-amps can fit into any of the STX II's DIP-8 slots.
 
You might also consider to just getting three LME49720NA (DIP-8) op-amps, for all three slots.
For the Buffer slot, you can switch between the LE49720NA and the Muse8920 and see which you like better