Sorry to hear about your father's diagnosis. One comment of the diagnosis, you said:
but you also said:
If nothing was felt on the DRE and no further imaging was done, he is stage T1c. The stage is not based on the pre-treatment biopsy, if that was a supposition on your part. The reason this is important is that stage T1c together with PSA under 10 and Gleason 6 squarely puts him in the low risk category. This makes sense, since his doctor recommended Active Surveillance.
PC like your father's is typically slow growing, so he has lots of time to explore options, including getting on an AS program.
In addition to AS, he may be a candidate for hemi-ablation -- getting rid of the right side of the gland only.
In terms of permanent cure rates for low risk disease, all of the following, if done at centers of excellence, are in the 95% cure range (as measured by freedom from biochemical (PSA) failure after 5 years): surgery (robotic, laparoscopic or open), HDR brachytherapy monotherapy, CyberKnife, and LDR brachytherapy (seeds). IGRT/IMRT and standard proton therapy are almost as good. Pencil beam proton (available at MD Anderson and UF Jacksonville) is very promising after a couple of years.
As your father learned from his friends, surgery is certainly the most popular option with about 70% of newly diagnosed men electing to have it. Surgery is also the most problematic in terms of side effects: incontinence, impotence, etc. "Nerve sparing" reflects a wish on the surgeon's part -- small nerves have to be severed -- sometimes they grow back, sometimes they don't.
The kinds of radiation therapy I mentioned as being the most curative (CyberKnife and brachys) also have the least side effects. There is no reason to have hormone therapy along with any of them, especially for low risk disease.
Urologists are usually ill-informed about the various radiation therapies, their cure rates and side effects. Unfortunately, you will have to talk to radiation oncologists in each of those specialties to gain a proper prospective. I went through five urologists and radiation oncologists before deciding. Fortunately, your father has the time to do so.