The VLX uses basically two USA-400 boards but there are differences between the two. Nothing drastic really but I doubt a VLX and a USA-400 would be sonically and they are not completely the same as far as the build. If you don't believe me look at the pics on amp guts and you'll see the most obvious difference which is the fact that the VLX is missing a row of caps on the first board. There are other differences but its not worth arguing about. I would love to own a VL-400 myself, because they are half the size and much more practical.