Thank YOU for the very helpful impressions! I'm glad I could introduce you to the song too, the entire album ("Mezzanine" by Massive Attack) is awesome too, maybe even a top 10 album for me.
@sm0rf @azertyproxy Thanks a lot for these impressions of Monarch OG vs. VX and vs. Monarch MkII respectively as well!
So this sort of tracks with what I was expecting, which is that the VX (maybe by extension the V14 too? Though I've heard that one actually has a bit more subbass than the VX) can't really be a strict upgrade to the Monarch in terms of being an IEM bass cannon. Which to me is arguably the single thing that is the most special about the Monarch - there are a lot of highly-resolving, neutral-tuned, excellent IEMs, but not many that are all of that with a random slab of massive subbass attached. I like the way it was described in this thread a few pages back - they feel like a "statement" piece with a unique audio vision, rather than an arms race to the highest detail with the most natural tuning.
But like you mentioned in your edit, the U12t is also on the table as a subbass-focused upgrade and I've been looking into that a bit as well. And then of course there's the Monarch MkII with similar subbass but apparently dialed back a bit and in exchange, a bit more resolution and technical performance across the board (along with fixing the midbass wankery on the Monarch out of the box, which to be fair can already be EQ'd away).
If I can swing it, the solution might be not "upgrading" the Monarch at all, but rather keeping it as a side-piece specifically for genres that sound great with bass cannons, and then having another companion daily driver that has better technical performance.
So I think the game plan here is:
1. Compare the Monarch to the Monarch MkII and if the subbass performance is still in an acceptable range on the MkII, replace the OG with it;
2. Compare the Monarch/MkII to the U12t and keep whichever sounds better to my ears, notably in terms of subbass extension and quality;
3. Compare the Monarch MkII to the VX and only keep the VX if it has a better technical performance to an extent that I feel is commensurate to the price premium.
This involves four IEMs and three of them are kilobuck+ so this will be quite expensive, but I'll see what I can do and I'll treat it as a longer-term thing. It's not like I'm desperate anyway, I could very much drop it all and just keep listening to the Monarch everyday, because it is awesome. But then again, if I could honestly do that, I wouldn't be on Head-Fi LOL.
If you do get a U12t and post any impressions of U12t subbass compared to the Monarch, I will read them with great interest and appreciation!