Shane,
Dan is a friend of mine. I'll get his email address to you later tonight. I've been working a couple projects with him, and he's helped me out with my Buff Minorcas as well. You've identified a couple items relative to color that are the real gotchas in the Buff color. I raise Buff birds in several breeds, Plymouth Rocks (Large and Bantam), Cochins (Large and Bantam), Large Fowl Minorcas and Leghorns, and Buff Wyandotte Bantams.
I try to never use a bird with white anywhere in the surface of the feather. Specifically in the Leghorns, I've had pullets with white in the tails as well as males showing white in their main sickles. I try not to use a pullet showing any white whatsoever, but will forgive a male that fault (main sickle) if the type is acceptable. Ultimately you wouldn't want to use a bird with white. Focus on the undercolor and the primary quills. If you can get good buff undercolor and nice buff quills all the way to the base of the feather (or at least fairly far down the shaft of the feather), you have a good chance of having a good colored Buff bird. I breed my Buffs to be a bit richer in color than some tend to like, and again, this avoids white. I will also use a female with some smut in her tail as this lends to good undercolor and seems to keep an even shade. Try not to use a male that is darker in the shoulders and across the back compared to the hackle and saddle, but if you have to use one match him to a female as even in color as you can. A good rule of thumb is to match the color of the female to the breast color of the male to maintain evenness of color. You can use birds that differ in shades but again, don't go too drastic on the first cross.
My question for you is how is the type on your foundation stock? Are they good in size and station? If not you may need to cross to another variety that carries better type in Australia.
I'll try to take some pics over the weekend and post.
Tom