asus stxII with sparkos discrete opamps

The STX II uses two MUSES 8920 for the DAC I/V stage. These have a slew rate of 25V/us (on the fast side).

However, the output opamp is a MUSES 8820 (outputs to the RCA connectors) has a rather slow slew rate of 5V/us. This will roll off the high frequencies rather drastically.

The OPA827 op amps (that I recommended) have a slew rate of 28V/us, but they are actually very excellent sounding with good bass and great resolution for a monolithic op amp.  They are also more forgiving and easier to implement than other "touchy" op amps, such as the more expensive OPA627 (slew rate 55V/us, but requires 0.1uf MKP capacitor soldered directly across power pins for stability) and stuff like OPA211 (which is a very sharp op amp, but actually came across somewhat bright and harsh).

You could also try the new Burson V6 Vivid op amps.  They are better, sharper and much higher resolution than OPA827, but they -could- have a possibility of coming across slightly thin/harsh in some systems without good power supply.  I would say to try the OPA827 first and if they are still too slow/dull, go for the Burson V6 Vivid.

By the way, I have tried and worked with a great many op amps over the years trying to find the best configuration.  I have ended up running a combination of Burson V6 Vivid fet-based op amps and Sonic Imagery 994Enh bipolar op amps (not recommended for your STX!!!!).

The Burson's are excellent resolution and have a slightly warm character, even though high frequency resolution is amazing.  The Sonic Imagery are the most demanding on the power supply and are just HUGE op amps (requires space).  They also require big capacitors soldered directly onto the op amp for power supply and a very strong main power supply, but they are absolutely amazing sounding!   It's like putting a mini-Krell analog circuit into your DAC/preamp for $94 per dual-channel op amp circuit!  Both Burson and Sonic Imagery are fully discrete Class A analog circuits.

Thanks so much for the recommendation. I finally got the 827’s through soldered onto adaptors, sounds really good. A dark kind of sound, detailed, strong bass.
While i was waiting for the 827’s, and after doing some searching, I played around with the stock 8920 x 2 in the i/v, and the 8820 in the buffer.
The treble was muffled.
But when the 8820’s were switched around into the i/v and the 8920 was moved into the buffer, there was no more muffled treble.The treble muffling of the 8820’s was only there when placed in the buffer, not in the i/v.So does this mean that the characteristics of the opamp in the buffer dominates. That i can shove any old opamp in the i/v, but the buffer one must be of high quality to allow the correct sound signature to come through. It might save me a lot of money in the future to use cheap, readily available opamps as long as they do not degrade the sound.
Many thanks

In my experience, op amps even in the I/V position will affect the sonic signature.  However, the I/V op amps are placed right at the DAC chip output.  The DAC chip is outputting straight DC pulses.  These are essentially square waveforms.  The purpose of the I/V stage is to amplify these square waveforms and also provide some sort of smoothing to turn these into the curved analog waveforms of true sound.  The slow slew rate of the 8820 may be helping to smooth these straight line square waveform pulses.  On the buffer output stage, the waveform is already somewhat smoothed, so the slow slew rate is having even more of an effect to reduce the high frequency response.

Sorry, got a little lost, my knowledge is not as good as yours.

Are you saying that a slow slew rate may be advantageous in the i/v position and a fast slew rate may be advantageous in the buffer.
With the stock configuration of 8820 in the buffer and 8920's in the i/v the bass and mid are both excellent, the treble is reduced with poor detail.
With 8920 in the buffer and 8820 in the i/v the treble detail has returned, but the quality of the mid and bass has lowered, does not have that warm tube like sound of stock.
Am trying to undersand why this is happening, trying to get the best of both configurations but struggling.
Thanks!