What to say? I think we had many good tries today, so I don't want to announce a single winner, but three: @pompe72 was the first one who nearly solved the problem, just was missing the fastest finish. @gaby-de-wilde finally found the complete solution and @afrog helped @pompe72 to finish his attack. Good teamwork. Congrats, the problem is solved now! :) Complete solution:

1. ... Rxa2+
2. Kxa2 c1N+
3. Ka1 Nxb3+
4. Ka2 Nc1+
5. Ka3 Ra8+
6. Bxa8 Qxa8#