Will,
I use just about the same soil mix for almost all trees. Hundreds of trees, mind you, some extremely valuable. I do not think that it is worth to bother about individual mixes for every species.
I take whatever the garden has available:
for most conifers and rather dry loving trees:
80 % pumice or 'turface' or lava split, or akadama or similar of a mixture of all these
20 % peat
for non-conifers (broadleaved trees) and some conifers like spruce:
60 % see above
40 % peat
no compost, no other organic ingredients.
For azaleas and other ericaceous plants:
100 % kanuma or 50 % peat and 50 % pumice
There are no nutrients in my soil. I have to feed on a regular basis, mainly organic.
The soil is very well draining but dries out quickly. I have to water EVERY day, in summer twice.
best regards
Walter Pall
http://walter-pall.de look how healthy my trees look with this simple soil regime.