With less price of the megaladon you can get the Siberia V2 with the 7.1 surround soundcard like you said,Personally I got the siberia v2 with the soundcard too and I love it,I got it when it wasn't even being sold in malta because it got amazing sound,and you can tweak it with the soundcard software.
So yeh it's your choice,I like the roccat too,probably if it was out the time I bought this headset I would of got it instead,not because of the sound,just because of it's style.Because the siberia is 7.1.
Btw for the roccat you need a good soundcard,because you need to connect all the 4 jacks to fully enjoy it,not only the green jack and usb 