At my university all of us playing Alto-Guitar used Savarez Alliance,
normal tension (which is much harder than "normal" normal tension)
for the first 6 strings. I acctually used corum basses for 4-6 like
Dave for a while, but I didn't like the lower tension they had, so I
switched back to the normal Savarez Alliance set with standard
basses.

The best sollution for the first six strings I have ever tried is
Savarez Alliance normal tension for 1-3 and D'addario Pro Arté,
normal or high tension, for 4-6. Then I use the hannabach alto-guitar
set for the lower 5 basses. These strings are of higher diameter than
normal basses. Some people use e-strings for all the basses, it works
but it doesn't give nearly as deep sound as the hannabach set. I'll
see if I can find a link later on for these strings. But you should
be able to order them from Hannabach.

Also, since the guitar is rather thick and hard in it self, alliance
trebles will really get the top swinging. I've tried a few normal
nylon trebles but the sound is to thin for my taste.

Right now I don't have any diagrams of the guitar. But I'll see if I
can get my hands on some...

I hope this nerdy post helps. Remember that the string issue is a
matter of taste and instrument. Try out what other alto-players use
and experiment to find your dream-sound.