I agree that at that price point, it's a matter of taste and although I liked the S-EM6 the week I had it and listened 6 hours a day (was on vacation), I found it not bright enough (although with a lot of detail) and with very different result accross masters. It doesn't forgive bad mastering.
Contrary to what people might think, bass is not the differentiating factor. The S-EM6 has nice, well extended and well defined basses and they're probably a tad more punchy than the S846. Now sub bass perf on SE846 mean they extend further like no other, but it's not applicable to every genre. The SE846 bring more transparency and clarify (especially wit the bright filter, the warm filter is the closest to the sound you'll get with S-EM6). I like timbre better on those too. You need to be careful to test a burnt in SE846, really I never said that for any other BA IEM but those *really* get better after 40, then 80 and 160 hours.
Whichever you pick indeed it's a matter of sound sig but also source as the higher end you IEMs, the higher end the source need to be (AMP/DAC), the difference with lesser IEMs is they scale up in a big way IMHO. On this the filter system on the SE846 gives you 3 different sound sig (neutral being the less impressive of all, bright and warm really are something special).