The VOG is available in the original 500 series format and now in a standalone format, the I-VOG (in the same chassis most little labs products come in).  The I-VOG does add a very hi Z instrument input (3.32 meg ohm), this was a natural because the circuit on its own is naturally very high impedance. Wait til you try plugging an instrument in here, you're going to dig it, and nobody really knows about that feature yet...Also you have the VOG available in a UA platfrom plug in.  This requires a UAD-2 card, but these are well worth it, all the plug ins they offer are top notch!