The CA CIEM are sensitive to hiss and it's difficult to have a perfect black hole behind the stage. The Headamp Pico Slim is perfect to do that job, I don't know the Arrow but I know that I love my Pico that can purify the signal and push the power most of the CIEM need to be more enjoyable.
The Music One are one of the best IEM I ever heard in terms of natural sounding, except that the sound signature has a bump in the high mids that is absolutely non aggressive and make the CA sound signature sounding lovely. Currently I prefer my Music One to my pro330, the soundstage is perhaps more in the head, the separation of the instrument is less airy, but it's more enjoyable, they sound good on poor tracks, perfect on excellent quality tracks and they have bass like any other mono BA I've ever heard. Just astonishing.
The Music Two is more open sounding, airy and keep the sound signature of the Music One with a better layering and instrument texture. Oh yes I forgot it, the instrument texture on the Music One is that texture you could have uniquely on CIEM. I just heard that kind of texture on CIEM and no one IEM could do that, except IEM that are CIEM based. The Westone 4 are less textured than the Music One. The SM64 are near from that. Okay, sorry, the Music Two is even more interesting than the Music One to my mind, it's a real upgrade to them and if you want a CIEM that can perform with much better CIEM, buy them.
The pro330 is clearly a professional CIEM, more flat and balanced, less enjoyable on poor tracks, they are less "aggressive" too on dynamic tracks. They cost 575€ but to my mind they could be pricier, really. I compare them with my EM32 that are 1000€ CIEM, almost twice the price and they are not so far, except that the EM32 could be pricier too considering they compete at this price with CIEM and IEM that are not as good (technically) than the EM32. I love the mids on pro330 that give the feeling you have a real soundstage with a superb sensation of deepness. They are a little veiled compared with the EM32 mids but to my mind no one CIEM at this price level could compete.
To my mind Piotr, if you are tuning the Harmony, don't use the philosophy of the pro330 but this for your Music serie. I regret that the pro330 are so rigorous
I don't have FB too, but I can follow Piotr on his FB page thanks it's open to anyone : https://www.facebook.com/thecustomart