Hi, Kara,
-:¦:-•:*'""*:•.-:¦:-•*Welcome to MyMigraineConnection!*•-:¦:-•:*'""*:•.-:¦:-
Research has been discovering and teaching us more and more about medication overuse headahce (MOH), aka rebound. In fact, were I to write my book today, I'd need to change parts of the section about MOH.
It used to be thought that we could alternate classes of medications, as you described, to avoid MOH. More current information shows us that this can lead to MOH too. 
I recently rewrote the MOH article here to reflect the newer information. I hope you'll take time to read the article Medication Overuse Headache: When the Remedy Backfires. In particular, note this section from the second page of the article:
8.2.6 Medication-overuse headache attributed to combination of acute medications
Intake of any combination of ergotamine, triptans, analgesics and/or opioids on 10 or more days/month on a regular basis for more than 3 months without overuse of any single class alone.
If you're still referring to my book for information, may I suggest that you print this article fold it, and stick it in the book so you'll have the most current information?
Most doctors are still saying we should limit "acute" medications, those we take to relieve a Migraine, to no more than two or three days a week.
Usually, using no acute meds for two weeks will "reset" our system and stop the MOH, but this can vary from person to person.
One thing to note is that even if we're at our limit of days for Migraine abortives and pain medications for the week, we can probably still take an antinausea medication to relieve nausea, if it occurs, and that will often also help us releax and, hopefully, sleep. Sleep is a natural Migraine abortive.
Once you're read the updated article, please let me know if you have more questions?
Welcome again,

Also - I don't think that it's a good idea to alternate medications. Right before I was forced to detox I was alternating Imitrex and Relpax because my headaches were so frequent that only one perscription wasn't enough to get me through the month. I'm not sure if the kind of preventative makes any different - your body is still being conditioned to expect medication everyday.