Len raises a good point about the possibility of using ambisonic microphones in the spaced positions, although in doing that the channel count requirement grows quickly. Extending the center coincident + spaced pair arrangement by using 1st order ambisonic microphone in all three positions would require 12 channels. Used in the spaced positions to either side of a standard 2ch coincident pair in the center, 10 channels. It is a very attractive proposition to be able to vary angle and pattern of the wide spaced positions on mixdown however, with full control over angle and pattern, and the ability to derive both front and rear-facing spaced pairs.
A more productive use for 8 channels might be a single ambisonic microphone in the center between a spaced pair of omnis with each omni configured as a Strauss-packet (a coincident 2ch arrangement of an omni and a forward facing fig-8). That provides full ambisonic coincident center, along with choice of pattern and of pointing the spaced pair forward or backward (or both), lacking only fine angle adjustment over the spaced pair. Maximal flexibility within a practical limit of 8 channels, while still retaining the basic 3-point arrangement of coincident center + spaced pair.
The all-ambisonic approach when limited to 8 channels would either be a spaced pair of 1st order ambisonic microphones, sampling 2-points in space (perhaps optimal for head-tracked binaural if limited to 8ch?), or a single higher spatial resolution 2nd order ambisonic microphone such as the OctoMic, which would be limited to sampling a single-point in space.
I currently sort of go the opposite way, using an 8ch OMT8 array primarily based on spacing, sampling 7 separate in space with the center position being a coincident Mid/Side pair. I do have plans to try replacing 4 of those channels - the center Mid/Side and rear-facing near-spaced supercardioid pair - with the TetraMic in the center position at some point.
Not sure about harder, but that should be smaller and faster.. will it also be better and stronger, Daftpunk?