I have both the GR07 Mk2 and the BA200, and have listened to the IE800 before going for the BA200.
They're all a bit similar to the point where it's arguable if they'll compliment the GR07. But I'd go for the BA200 as it's dual BAs are noticeably faster and resolving for quick music like metal than the dynamic drivers in the GR07 and IE800 - who have more bass and are both slightly treble forward than the BA200. On the other hand, I feel the IE800 is less neutral and more colored than the BA200 and the Gr07 Mk2- so there's that too.
In what way do you wish to complement the GR07 Mk2, though? The BA200 is my current favourite IEM by a long way- but if you want something that truly complements the GR07, especially if you want more bass, sub-bass and oompf in the low-end for electronic music, or want to hear the the basslines in rock music more clearly, you should look into the XBA-30.