You listen to music very similar to me actually!
Also, thank you for your kind words!
If you have DX150 already, then getting AMP5, AMP8 or AMP4 for it may make more sense than getting DX120. The main drawback of DX150 for Meze 99C is the AMP module, which is a little too warm and too thicc / too smooth, given that Meze 99 are already quite thicc and smooth. This overemphasizes their signature, which I would normally EQ against by increasing the treble and decreasing the bass.
DX150 is better than DX120 in almost every way, including the DAC, so you can increase your fun and experience by getting a better AMP module rather than changing the whole DAP.