I agree that it's more than just the scalenes involved here. Probably the pectoralis minor is also in spasm, and so are the muscles that run along the side of your neck. When you look at http://www.carpaltunneltreatment.org
and then at the scalenes, you are only looking at the anterior scalenes. There are fibers on the very side and also the back of your neck that will hold your cervical vertebrae stiff when you try to turn in the opposite direction.
Also, the posterior neck muscles; splenius capitis and splenius cervicus, will prevent you from turning in the opposite direction, and they will refer pain all the way down the upper back, right next to your spine. They are the muscles that allow you to look up to the ceiling, and if they are tight you can't look down toward the floor.
Another muscle that is probably involved is the levator scapulae. This muscle raises your shoulder up, the nickname is "the shrug muscle." However, if the muscle is tight it will pull on the 3-6th cervical vertebrae and will also prevent you from turning in the opposite direction because they are too tight to lengthen during the turning of your head. It will also be beneficial for you to learn how to self treat the trapezius muscle since this one originates along the length of your cervical and thoracic spine. When it's tight, you can't turn toward the opposite side.
Do you have my book, either The Pain-Free Triathlete
or the new ebook Treat Yourself to Pain-Free Living
? Both of these books teach you how to treat the neck muscles, as well as the rest of the body.
It's important for you to learn how to self-treat these muscles Scott. You certainly don't want to have to take muscle relaxers frequently, they only mask the problem and don't cure it. You can work each of these muscles out, and by knowing how to do it, you could make it a part of your regular workout routine, especially when you've had an intense session.
Wishing you well,