GoRedwings19..you might find, as I did, that the Valhallas are not the best match with the R-10s. To me one significant difference between the R-10s and the HD650s using the Maestro was that the R-10s were voiced farther back in the hall. This voicing gave the R-10s the perspective of a larger and more coherent stage as well as giving the impression that the harmonic envelope had more space to unfold.
To me, part of the magic of the R-10s that I did not find in other headphones - and particularly the upper end Grados - was this ability to feel the harmoic envelope. The Grados are voiced, at least with all the amps I heard them with, very close. Harmonics need to open and decay correctly to sound "real".
Now the problem with the Valhallas was that they tend to move the voicing much closer - in a speaker based system, where you actually have space for harmonic bloom this is fine. But with the R-10s I did not care for this "projection" of voice that the Valhallas lent (even though I love the Vallhallas in the rest of my system).
I don't mean to ramble here but I will note that the Virtual Dynamics Master Series cable was preferable to the Valhallas IMHO for the R-10.
Further, I think I am in line with Dolifant about the upper end Grados. They are exciting and precussive. The have detail and in some cases musicality AND the have great attack and immediacy. But in the end I found them bothersome because they were voiced too close to the ear. You never really heard the harmonic develop and decay..I would point out that to many people, the harmoinc attack/expansion/decay are a coloration....but I believe a correct one. The R-10s also give the sense of fuller body than the HD650s or the Grados (again IMHO).
From what you are saying you will love the R-10s.....But I would not knee jerk into the Valhallas as they are expensive (and I say this as someone who uses Valhallas IC and speaker cables across the board in my 2 channel system). You might try different ICs you can borrow to find system synergy.