I have a Musician Monoceros preamp for which I don't have the remote, unfortunately.
By an incredible luck I have managed to get one IR code for POWER_DOWN. Basically, I saw that when my Samsung TV gets a new HDMI input, it sends some IR codes and one of them turns off the preamp.
I intercepted that code using a RPI and IR transceiver. Encoding is MCE and by playing a bit with irScrutinizer (D, S, F, T values variations), I managed to find some more codes.
However, I did not manage to find VOL_UP code and I am a bit stuck now. Of course, the most important functions are VOL_UP and VOL_DN.
I have to say that my knowledge regarding IR transmission is limited.

Here is what I have at the moment:
I am hoping that more knowledgeable people can help to find the VOL_UP code.

begin remote

name proper
flags RAW_CODES
eps 25
aeps 100
ptrail 0
repeat 0 0
gap 20921

begin raw_codes

name VOL_DN
2664 888 444 444 444 444 444 888
444 888 1332 888 444 444 444 444
444 444 444 444 444 444 444 444
444 444 888 444 444 444 444 444
444 444 444 444 444 888 444 444
444 444 888 888 444 444 888 444
444 888 444 444 888 888 888 888
888 888 444 444 444

name POWER_OFF
2664 888 444 444 444 444 444 888
444 888 1332 888 444 444 444 444
444 444 444 444 444 444 444 444
444 444 888 444 444 444 444 444
444 444 444 888 888 444 444 888
888 888 444 444 888 444 444 888
444 444 888 888 888 888 888 888
444 444 444

name PREV_SOURCE
2664 888 444 444 444 444 444 888
444 888 1332 888 444 444 444 444
444 444 444 444 444 444 444 444
444 444 888 444 444 444 444 888
888 444 444 444 444 888 444 444
888 888 444 444 888 444 444 888
444 444 888 888 888 888 888 888
444 444 444

name DIM-
2664 888 444 444 444 444 444 888
444 888 1332 888 444 444 444 444
444 444 444 444 444 444 444 444
444 444 888 444 444 444 444 888
888 444 444 444 444 444 444 888
888 888 444 444 888 444 444 888
444 444 888 888 888 888 888 888
444 444 444

end raw_codes
end remote

Thank you in advance,
Fabian

VOL_DN: MCE Device: 38.126 Function: 84

POWER_OFF: MCE Device: 38.125 Function: 84 T=1

PREV_SOURCE: MCE Device: 38.119 Function: 84

DIM-: MCE Device: 38.119 Function: 84 T=1

Since T is a toggle (every second time a signal with T=0 is sent, the other ones are sent with T=1), it is unlikely that the #3 and #4 really are different commands.

All the signals have D=38 and F=84, with S=126,125,119. So it would make sense to try a few signals with D=38, F=84, and varying S. Just ignore T.

After more playing around with the IR transmitter, I have found out that PREV_SOURCE and DIM- only work if they are sent one after another, not as single commands. The VOL_DN and POWER_OFF work as single commands and interact perfectly with the device.

I have tried all the S combinations with D=38, F=84, 256 of them. Unfortunately, nothing more happened than what I already have posted.

Could it be that the device is working on a different IR encoding, but somehow reads MCE encoded signals?

Still did not find volume up command, all thoughts are welcome.

The catch was that irScrutinizer was identifying the signal as MCE, when it actually is RC6-6-32. MCE D38 F84 S126 is exactly the same as RC6-6-32 D38 F84 M6 OEM1:128 OEM2:126. S from MCE goes to OEM2 from RC6-6-32. In case of MCE, OEM1 is fixed at 128 and M is fixed at 6.

Basically, what I did to find the volume up code was to play around with OEM1 from RC6-6-32 and voila, volume up is now working.