I'm in a somewhat similar situation, but my PSA level has not been quite as high as your husbands. I'm 48, good health. As you see from my signature below, my PSA has been from 4.8 to 5.4 recently, and free PSA has been 7% to 8%.
I read Dr. Walsh's book after my PSA test in July, and it scared the crap out of me. Particularly where he referenced the Baltimore Study on Aging, and taking a number of men who had developed agressive PCa and going back and looking at their stored blood samples from before they were diagnosed with PCa. In some cases these samples went back a decade before they were diagnosed, and everyone of those men had low free PSA long before they were diagnosed. So they say there's a 56% chance of having PCa with low free PSA, but I have not found any mention of the other 44% and what could cause low free PSA besides cancer. I posted here a few weeks ago, hoping someone could shed some light on it, got about the same response you did.
After my biopsy in October, the urologist called to tell me there was no sign of cancer, my prostate was enlarged, repeat the DRE and PSA test in 6 months and go from there. I have no symptoms of BPH. My GP did not want to wait 6 months (neither did I), repeated PSA test after 3 months and PSA dropped from 5.4 to 5.2, free PSa stayed at 7%. I have done a lot of searching on the internet for info on low free PSA, there is not a lot of info there. Could be there is cancer present, but it is so small or in such an awkward spot that a biopsy does not catch it. Could be free PSA is low for an unknown reason.
I do know there is work being done on new versions of the PSA test- they have found that free PSA is made up of several things, and they are looking at the individual components of free PSA to see if one of these is a better marker for PCa. Of course this is down the road a ways.
I found some interesting info about free PSA on the Fred Hutch Cancer Research Center (Seattle) web site, and Dr. Catalona's web site. I'll put a couple links below. If you do a search for "free PSA" on these sites you will find more info.
Like you, I'm trying not to dwell on this. Maybe its nothing. But the look on my GPs face when she gave me the first PSA results back in July, she was worked up and you would have thought she was telling me I had cancer right then. So I'll see the urologist again in March, repeat the PSA test before then, and unless there is a significant drop in the PSA and rise in free PSA, I'll expect another biopsy. This time I will pick his brain for more info on low free PSA. I would be very interested how things turn out for you guys, and if you come across any info on free PSA. Please post again. My e-mail address is available in my profile if you want to drop me line.