I've been listening to R35TT, which I believe contains some of their oldest available material and the difference between the songs on here and normal boc songs is that on most of the tracks on R35TT, the drums sound very acoustic whereas in later boc albums, the drums seem to mostly be synthesised. As well as this, the drum tracks on these earlier tracks seem to incorporate much more complex rhythmic structure compared to the actual released stuff (Twoism and MHTRTC especially) where drum tracks are very repetitive and simple. This suggests that Marcus and Mike were struggling to get any kind of rhythmic variety after the supposed drummer left. I believe it is common knowledge that Boards of Canada used to be composed of more people and from this, I believe one of them was an acoustic drummer, at least in my opinion. The brothers obviously struggled creating good rhythms for a while but seemed to get the hang of it whilst recording the many songs for Geogaddi. Just an idea, possibly totally incorrect but meh.