You're confusing 2 separate products which 3DR made...
1. The X8 was an 8-motor bird with 2 motors at each corner in a top-bottom arrangement.
2. The Solo is a 4 motor bird, with smart shots, and probably the most popular bird for folks on the forums here.
Now, strictly theoretically the flight controller in the Solo ['The Cube'] is fully capable of managing up to 8 motors. I don't know anyone who has attempted a conversion of a Solo frame to such though....