Microcomputers As A Space Spinoff 3839
Surely you're thinking of The Digital Group, out of Denver. I had the impression (I don't know from what, other than the name) that they might have started like a club, pooling together to buy parts and build computers for members, that morphed into a business. They used a bus that was not CPU-specific, unlike the S-100 bus that brought out many CPU lines that didn't fit other CPUs. And the plan was to make the hardware last longer, so when a new CPU came along you'd just buy a new board and plug it in rather than buy a new system. That would fit the poster's comment about not being an all in one system with multiple CPUs; you could either change boards when needed, or build up separate systems.
I already mentioned them in this thread, including the caveat that they did have a Z-80 (and I think the previous poster had said the company he was thinking of didn't), and as I recall, they had none of the "obscure" CPUs like the SC-MP that the previous poster had mentioned.
The Digital Group eventually had very neat looking cases, though I gather from reading that the casing came late and may have been relatively hard to come by.
Microcomputers As A Space Spinoff 3840
box one I liked the looks, and specs, for the OSI's but I never worked with one at all. I lusted after those...