Operation: Amp!
1, Tools: T5 driver, chip lifter, puller, and extractor.
2, opened back.
3, MUSES8820 pulled.
4, caution: make sure you lift and pull straight up, or else the pins are easily bent. Most of my chips pins are bent now, but the lifter can also use to help straighten the pins out. I recommend lifting the chip first then pull, as the socket can be pretty tight.
5, LPF Amp replaced.
Findings:
Test track: Christina Perry "Human" from "Heart to Heart" in 24/48 up sampled to DSD128.
1, sad to report that single channel amp like the OPA627AP does NOT work.
2, MUSES01 is under powered and sounded very dark, which makes the recessed mid issue worse.
3, MUSES02 is better and bring the SQ closer to neutral but still on the warm side, mid still recessed but not as much as the stock MUSES8820.
4, the most surprising is the LEM49860, which can be had for $5 for the pair. This amp is bright for the VC SounDroid Typhoon (which is also why I got one more to make a pair for the test.) However, pair with the warm AKM4490 DAC, the SQ balanced out and make the whole thing much more neutral, plus fixing the recessed mid to a large degree. This is not a 100% solution, but making classical more enjoyable now.
I am keeping the LEM49860 inside for now to compare to my AK380. Also, I am sad to report that my unit also developed the "white line" right after the amp swap with my OPA627AP.