I would like to make one very important point here.. because well, there is a certain amount of misinformation being shared.
There is no "best soil money can buy" per-se.... your soil mix is as much determined by your climate as overwintering means and watering patterns. If i tryed to keep trees in the most effective soil mix for some place like Nebraska or Texas I would be killing trees left and right. Living in a near rainforest requires me to use a very very fast training mix that doesn't hardly hold water.
Someplace like Nebraska (i would assume having grown up in Wyoming) would need a soil that would drain well but still retain a larger amount of water to withstand the hot dry summers. Otherwise you will be watering 4-5 or more times a day.
So when it comes to soil mixes the best bets are to check with others in your same region and see what mixes they use for their trees. Often times in certain climates different trees need different soil. This all boils down to providing each tree with the soil that is perfect for it in the climate in which you live. Just like fertilizer programs and watering programs are unique to trees often times soil can be as well.
Akadama is a great adative to soil mixtures and some people use it straight...but then again some people use straight diatenatious earth as well. So research and find what works best for you.
You can do a little research here on this forum and amongst others to see many of the great recipes used by members all over the world. There is an entire section on this forum regarding soils etc..
http://forum.bonsaitalk.com/f8/
At this stage in bonsai...you will do best to learn... read , read, read and when you think you have read everything.... read it all again....but most importantly.... NEVER EVER EVER EVER be afraid to DO...... there is no better way to learn in life than to do... and if you kill a tree or 50.... you'll only continue to learn more and be that much better for it.