There are other options as well. For example, discordant couples may want to consider adoption as one possible option. Adoption removes all the risks for HIV transmission, and at the same time, allows the couple to have a child. It also allows a child to have a new family. There are many children out there in need of a caring family.
Adoption therefore solves two issues at the same time.
In other words, they choose to have unprotected vaginal sex to impregnate the woman, despite the fact that this puts the woman at significant risk of infection. They then take their chances that the woman will not get infected. This is the riskiest and least desirable of your options, since this is the riskiest option, in terms of the woman and her baby becoming infected. Remember, there is a significant chance of infection during unprotected intercourse, even if the viral load of the man is low. If you are interested in sperm washing as a realistic option for you, I have a listing of research reports that have been published on this very topic.