Ok, so here are a few more impression. I'm not gonna go into too much detail as I'll leave that for my full written and video reviews.
This is also with reference to my HD58X as the entire idea for me was to try and find something similar to the 58X in a portable package. Of course, the 58X is not considered as a "reference class" type of signature, but I think it should be considered as an excellent signature when taking into account the price (even a double the price)
RY04 - fairly smooth signature, but sounds a little hollow (slightly recessed vocals). Lacks warmth and deeper bass notes. Sounds overall a bit mid-centric.
Edifier H180 - somewhat similar to RY04 in smoothness, but less of a hollow sound, more balanced overall...really good detail retrieval in cymbals.
RY4S - warmer than 58X, more bass especially a noticeable rumble in the sub-bass region, but bass overall is a bit too much for me (just a bit), lacks some finer details and some smoothness, but overall exceptionally impressive for the price.
Snow Lotus 1+ CE - also slight recess in the vocals, overall reasonably smooth
Snow Lotus 2.0 - quite punchy, but again has some recessed vocals (more than SL 1+ CE) that makes the sound overall seem more hollow which tilts more towards a bassy signature but lacks the sub-bass found on the RY4S.
GM500 - most expensive earbud in this group, but sounds the worst to me. Has the most recessed vocals, less treble extension than the SL 2.0
At first I thought I preferred the SL 2.0 over the 1+ CE, but after comparing them directly with the 58X the 1+ CE is closer. If I could get the smoothness of the 1+ CE with the bit more forward vocals and deeper bass extension (but not overall bass level) of the RY4S, I'd be very happy. But, for now, i think the RY4S is my favourite so far.
Looking forward to receiving my next bunch of buds.