Wow! Epic conquest.
From the looks, the Umax is an S900.
That is something in between an 8500 and 9500 clone.
It has six PCI slots. No on-board video, so it is like a 9500 in that regard. However, the lower four PCI slots (slots 3 - 6) are controlled by a PCI-PCI bridge chip installed in place of PCI slot 3, instead of having their own Bandit chip.
So, a normal 9500 has two Bandit chips and they control slots 1 - 3 and slots 4 - 6 respectively.
And S900 has a single Bandit chip, which would ordinarily control just slots 1 - 3 (like an 8500). However, in the S900, slot 3's connection to the Bandit chip is usurped and the upstream side of a DEC 21052 chip is connected there. Then the downstream side of the PCI-PCI Bridge chip is used to create slots 3 - 6.
If you try to install a card which has its own PCI-PCI bridge (such as a USB/FW card) in slots 3 - 6 the machine will likely lock up at a black screen after the start-up chord. However, there are a lot of caveats to that which I'm not going to cover in depth. The main one is that the above configuration will work, provided there are no other cards in slots 3 - 6. Other conditions apply.
The S900 also has a second CPU slot for Umax secondary processor card, which supported their dual 604e configurations. And there's a jumper position (or an actual jumper) on the logic board which will disable the logic board L2 cache -- handy for G3 cards with their own on-board L2 cache.
Oh, and front and back sound ports which are nice, until you try to install the logic board in a different case.
The case is interesting. It is a Palo Alto Products ATCX Convertible. This case was also used by Micron and Dell in various models, with their own Bezels. The same case is also used in the Desktop Umax J700 model. By switching the bezel and the bottom/right panel of the case, and by unscrewing and rotating the internal drive cage, the case changes from a tower to a desktop.
The J700 logic board is identical to the S900 except it lacks the secondary CPU slot (connector is missing) and two of the lower four PCI slots. If the connectors are soldered into place, the J700 gains the same functionality as the S900.