Since AMD has released new Catalyst 15.7 WHQL driver, they have made it possible to CrossFire their previous R9 200 series cards with the new R9 300 series cards with one based on a similar-spec GPU from the R9 200 series. This is made possible by unifying the driver to allow CrossFire between an R9 290 or 290X with an R9 390 or R9 390X. This cross-generation pairing is nothing new for AMD as we have seen before with CrossFire between the R9 280 and HD7900 series and between R9 270 with the HD7800 series GPU’s.
It may even be possible to create a 4-way CrossFire with one each of the four cards. You may already know that with the newer cards that feature AMDs XDMA CrossFire, it is now possible to do away with the CrossFire bridges for increased flexability.
To can see demostrations of the new AMD Catalyst 15.7 WHQL driver and these new CrossFire pairings at Videocardz.