I ended up buying one of these, from this seller, and I have to say that after some work setting it up it was worth it. I really like my new Cherry MX Brown matrix layout keyboard!
The software is a POS. Key assignment is very clumsy, and it only runs on XP (so I needed to install XP and set up a dual boot to get it running). However, the only keys that cannot be assigned from a standard keyboard are the win and app keys (which I don't miss so much). Now that it's set up it works very well. It's connected by PS/2, so I have no problems in BIOS.
Keep in mind that when using a double/quad key, it will be much stiffer to press, since it's supported by multiple switches. I solved this issue by cutting down the springs under these switches to 10mm, which gets just about the right amount of force on the double keycaps.
This created another problem, since when a double key is placed on two switches with cut springs, it doesn't rebound properly 100% of the time. This is because the double key puts sideways pressure on the switches, which the lighter springs have a hard time overcoming. I solved this issue by widening the cruciform on one side of the keycap (by scraping some plastic out) - essentially the double keycap now only attaches to the switch on one side. So, those double keys feel good now, but it took some work to get it there.
The layout I'm using I'm very proud of - I made a split layout similar to a humble hacker. I decided to try out using left thumb modifiers (after a week I can capitalize faster, I'm still getting used to the ctrl hotkeys, though). I moved the + and - keys to the left pinky from the right pinky (which, IMO, is vastly overused on a standard layout). Also, I moved the navigation keys, number pad, tab, backspace and enter to sit in between the alphanumeric split. I especially like the new backspace location, since I can spam it really fast with my right index finger, while leaving my right pinky on the home row. One other thing - I moved the 1 and 0 keys down a row to make them more accessible for my pinkys, which are unfortunately shorter than my other fingers.
I took the keys from an old and very used G80-8113, which probably should have been cleaned first, but I was anxious to play with my new keyboard. The relengendable keys aren't great, but I'm too cheap to order a full set of custom double shots for this project anyways. Maybe I'll get lucky and find a used Access keyboard with just the right doubleshots to make this keyboard look nice, but I don't really care that much, anyway. I do use Colemak, which complicates finding the right doubleshots.
I attached a pic so you can see what I'm talking about. The left double key is shift and the right double key is space, those are unmarked at the moment. Also, I apologize for the poor quality of the picture - it was rushed.
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