What do you use your LGU for? If mostly target work or small pesting, reducing power with a different spring and a good fitting guide will make a pleasant difference. Look for more information over on the German airgun gate. If you didn't care about sacrificing your original spring and have the tools, you can cut iff a coil or two and try that.
I just want to point out shooter perceived sound can be different from muzzle report down range. This point was clear when I owned my first AA ProSport and AA S200, but in .177 about 12 FPE.The ProSport sounded quite loud compared to the S200. However, recording the muzzle report with a microphone and analyzing the waveform, I found that both guns have about the same muzzle report. The S200 did have a muzzle device to help quiet things down.Fast forwarding to the OP's question, the LGU has a larger chamber than the ProSport (but the ProSport is baffled), so it should quiet down muzzle report a little more than the ProSport. I think it is already quite quiet in terms of muzzle report, but the mechanical sound is always going to be there.