Most sound cards feature ADAT ports, so I made an 8 channel fader box with some Penny & Giles faders, and a d-sub 25 pin connector to make use of these extra channels. The design was based around the Fostex VC-8 ADAT interface since it has unbalanced phono connections for input and output, input impedance of 20k, and output impedance of 10k, making it suitable for the P&G single-ended faders without having to build buffers and other active circuitry.
In conjunction with various different applications such as Max/MSP it is now possible to use high quality analogue faders as precise parameter controllers. The easiest way to do this is to route a constant audio signal to each ADAT output, and then use an envelope follower on the inputs to derive a control signal. The VC-8 has 20 bit resolution, which is a lot better than MIDI, and more accurate than you'll ever need.
The aluminium was ordered cut to size so that the box would have an absolute minimum size. The faceplate was made by laser cutting a laminated PVC sheet. The faders are high quality and therefore a bit heavy, but it's a solid box and couldn't really be any smaller without sacrificing quality.
In conjunction with a Metric Halo sound card it should be easy to set up the faders as Bus controllers and parameter controllers for effects in whatever configuration is required.