Bill,
I ran your photo (from the BMP you sent me) on a product called Laser IT (
http://www.idplates.com/product?id=1428-1). It was a bit dark, like what you are getting on the AlumaMark. But it was also a bit dark on wood, as well.
I took your original and played with it. I made it considerably brighter (+83 brightness in Photoshop) before running the Gold Method. I got very nice results (photos to come this weekend). I did the same thing with some of my photos (greatly increasing brightness and then running Gold Method). These also gave much better results than I was used to getting.
On the LaserIT, I ran 300 mm/s at something between 25% and 40% (can't remember).
You might want to try LaserIT - as it is very reasonable in price - $6 for 12x24 and gives really nice results - I have used it for a couple of years now. They have a $75 minimum BUT you can call and give a credit card and they wave the minimum order requirement/fee.
Here are some tests I ran on LaserIT from IDPlates.com. I'm happy with it. (The discoloration in lower right corner is my shadow.)