Tried and hassled too much with
MultiWAN : Loadbalancing TCP connections over several lines. Each stream is limited by the 50/10 MBit/s of your connection.
Wanna go for it. Don't know if it is worth doing it
MPTCP-VPS : One TCP connection is split into peaces and transmitted via multiple DSL-Lines to a virtual private server (VPS) and combined there. However, you can say that your bandwidth of the tcp connection is approx the combination of your DSL-Connections.