The other fairly critical line (though less critical than 5...Bb4) is 5...d6 6.Bc4 Nf6, when play can continue 7.Qb3 Qd7 8.Ng5 Ne5 9.Bb5 c6 10.f4 Neg4 (or 10...cxb5 11.fxe5 dxe5 12.Be3 a5! 13.0-0 a4! 14.Qxb5 with complicated and roughly equal play, 10...h6 is relatively unexplored) and there are well-analysed complications stemming from 11.h3 cxb5 12.hxg4, and 11.Be2 h6 12.Nf3 d5 13.h3 dxe4 14.Ng1, where it's Black who sacrifices a piece for compensation. Black should probably avoid 10...Ng6 11.e5 h6 12.exf6 hxg5 13.0-0, which gives White a very strong attack. White can deviate with 7.Ng5 Ne5 8.Bb3 h6 9.f4, which is also complicated and roughly equal.
After 5.Bc4 cxb2 6.Bxb2, perhaps most critical is 6...Bb4+ 7.Nc3 Nf6. I posted some analysis which aimed to revive the relatively unexplored 8.0-0 in another recent thread, while 8.Qc2 d6 9.0-0-0 0-0 10.e5 Ng4 11.h4 Ncxe5 is dangerous for Black OTB, but theoretically it's White who is coming up short.
The other critical line is 6...d6, analysed in detail by John Watson in his review of Danish Dynamite:
http://www.chess.co.uk/twic/john-watson-reviews/danish-dynamite My preference has always been 7.Qb3, as I agree with his opinion of 7.Nc3 Be7 8.Qb3 Nh6 9.Nd5 0-0, and while I'm not convinced that Black is better in the line 7.0-0 Be6 8.Bxe6 fxe6 9.Qb3 Qd7 10.Ng5 Nd8 11.f4 Nf6 12.Nd2 Be7 13.e5 dxe5 14.fxe5 Nd5, it's also not clear if White's compensation is quite worth the two pawns.
In the 7.Qb3 line 7...Be6!? is interesting, as someone pointed out in another thread, as it's unclear if White has anything better than to transpose back to the 7.0-0 line after 8.Bxe6 fxe6 with 9.0-0 (9.Nc3 and 9.Nbd2 are also interesting, but 9.Qxb7 and 9.Qxe6+ Qe7 10.Qf5 slow down White's initiative too much). Black's main response is 7...Qd7 8.Bc3 (8.Ng5 Nh6 9.Bc3 is also interesting) 8...Nh6, when while I think Watson's analysis is impressive, I'm not convinced that Black stands better (e.g. 10.Na3 is interesting, and I think White still has play in his line 9...f6 10.Nbd2 Nce5 11.Nxe5 Nxe5 12.Be2 Qf7). Similarly, I'm not convinced that Black stands clearly better after 7...Nh6 8.Bc3 (8.Na3 may be a better bet, it seemed to me that ...b5 in Watson's lines could be met by the risky Nxb5) 8...Qe7 9.0-0 Ng4 10.Nbd2 Nge5 11.Bd5 Nd8 12.Nc4.