How can I help my husband de-stress so we can have better chances at conception?

Live him alone. If you are having difficulties achieving pregnancy and you need to have sex during the most fertile part of the cycle i understand the stress. Unless mandated by specialist dont think about it or he would get " performance anxiety" with erectile dysfunction. Let him find ways to deal with stress on his own. The male brain do not accept counseling unless requested by him after many failedattempts.
Stay active. Exercise is a great way to relieve stress. Your body releases endorphins during exercise, which can help you feel calm. If you exercise 30 - 60 minutes a day, your stress levels can improve. When stressed, take 5 slow, deep breaths with your eyes closed, then roll your shoulders forward 5 times, then back 5 times. This will slow your heart rate and release tension in your neck and shoulders.
Dont be too serious. Many couples stop enjoying sex when they are trying to get pregnant. They lose the intimacy and "medicalize" the act. There is nothing sexy about timing intercourse around ovulation calendars and body temperature charts. Creating a baby together is amazing experience. Don't over think it. Just relax and have fun.