(Edit: typos...)
I own a V6S, and I also demoed the V8. And I guess I agree with you - V8 indeed performs better for bassy tracks, and appears to be more enjoyable than V6S when I listen to my Japanese anime tracks. I don't consider myself a basshead, but I prefer a sound signature with a little bit more bass, unless when I'm listening to classical music.
When I bought my V6S, V8 was not yet available. I was choosing between V6 and V6S. After hours of demoing, in the end I went for V6S - because there was a bit more bass and a wider soundstage. What I didn't realize when I was demoing was - there is a minor problem of sibilance on a few tracks for V6S. It took me awhile to get used to it.
But then, I was more impressed by the V8 when I got the chance to demo it - I felt that this was the CIEM I should have got. But I wouldn't say I regret getting V6S - it is still a very competent CIEM, which can handle a wider range of music.
Whether V6, V6S or V8 is better is still up for debate. Several of my friends preferred V6 - they felt that it was more coherent, balanced and clear. But I prefer an IEM which would give me a more enjoyable and engaging sound signature - which is what the V6S is giving me. (But I have also pledged U8
)