I have succeeded after numerous trial and errors to come to a stable MBWEWL.
Update Firmware to 01.02.06
Update Twonky to 6.0.31
Now the box is very stable. Uptime is 2 weeks and counting.
With respect to performance it is clear that Twonky eats ALL the ‘power’ so when TimeMachine kicks in or you need to copy large files quickly then it is enough to SSH to the box and kill Twonky.