Well, yes and no. The SBM1 could be great at 16 bits, but have too much inherent noise as part of its design to get anything useful at 24 bits. That is, the increased 8 bits of resolution would just be essentially random due to the noise, and not capturing the true audio signal. That would explain why a box could be good at 16 bits, but not worth it to be expanded to 24 bits. But if those additional 8 bits are only capturing noise, what would be the point of dithering and noise-shaping from 24 bits to 16 bits?
At any rate, it doesn't sound like the SBM1 is going to be a candidate for a 24-bit A/D, even if the mods could be easily done.