There are two versions of in_vgm 0.35. One is the original in_vgm 0.35 by Maxim and one is called in_vgm 0.35 beta which is by me, Valley Bell. (and this one is actually newer)
Only the "new" version supports the SegaCD PCM chip. (and Audio Overload doesn't support these VGMs at all)
The size of the right in_vgm plugin should have 350-400 KB.
Sorry for the confusion. I'm working already on in_vgm 0.40 and when I release it, the confusion about 2 versions in_vgm 0.35 and 0.35 beta should stop.
You can get the right version here