I -almost- ordered an AMG S63 Cabriolet after spending a couple of days with an S63 Coupe. However, the seating position (I'm quite tall) puts me so that I cannot see the gauges well, the steering wheel is in the way, and I sort of look into the very top of the window.

I'm imagining not, but is there anything can be done to lower the seating position at all beyond the adjustments provided?

Don't know if the seat (rails) can be lowered more than standard, but I am sure you are aware (and tried) the electric adjustment of the steering wheel itself? It can me moved in 2 dimensions (up/down and forward/backwards).