A Closer Look - Inside
You have to remove a pair of screws and pry the metal mesh cover off to gain access to the case. Its internals only hold the I/O, the case's cables, the PSU converter PCB, and the area for the mini-ITX board. It would have been a nice touch to have an all-black interior, but you will not see much of the metal frame anyways.
Turning the chassis upside down, there are the two 2.5" HDD bays below the mainboard. You can easily install them after inserting the ITX board, but you may find it troublesome to route the power and data cables properly which is why I suggest you go for these drives first.
All the I/O cables are firmly fused together into one big, black block. It would have been good to see a detachable approach instead so that one could remove unwanted leads, or to replace a USB 3.0 cable at the end of the motherboard with one featuring a USB 2.0 plug. The PSU converter board is still exactly the same as the one in the original Antec ISK 100.
It carries the label "MD-80" along with Antec's branding. Looking at the underside, it actually states what the unit is capable of. The single 12V rail can deliver up to 5 A, while the entire PCB is made to push up to 80W, so you should not use components that draw more than 80W, although the PSU brick is intended for up to 90W.
All the cables within the ISK-100 are quite ordinary, but are actually rather long. These are probably the shortest ones that Antec had at their disposal without ordering custom ones for this chassis. They, ultimately, do work. I do believe it would have been a good time to upgrade the case to USB 3.0 since many mini-ITX boards also come with a 20-pin connector.