Hi Alexxx,
I just realized, you should take a look at AD8475 as well for the single-ended to differential converter. It's a differential output amplifier with integrated resistors AND it can be set to attenuate a signal by a factor of 0.4X. If you were to use the AD8428 and the AD8475 together, you would end up with a precise gain of 800, just like you were looking for. Both of these parts have more bandwidth than you will probably want, but they also both have pins that you can place a capacitor across in order to reduce the bandwidth.
Regards,
Scott