is consistent with the idea that the woman should be considered a wife, as opposed to a sex slave.

We have established that one human life is worth less than the other, slave and master. We have also established that god values women less than men. What exactly do you think happens to these women? They are all just willing to submit sexually?

However, verse 8 does go on to say that the "master" must let her go free if he fails to treat her as a wife, regardless of how long she's "served".

Wrong.

Here is the verse:

If she is displeasing in the eyes of her master who had designated her for himself, he must allow her to be redeemed.

So again it is up to the slaver to decide what to do with his property.

Ancient slavery was much more akin to an employer/employee relationship

Really? God clearly forbids?

When a man strikes his male or female slave with a rod so hard that the slave dies under his hand, he shall be punished. If, however, the slave survives for a day or two, he is not to be punished, since the slave is his own property.

Not exactly like your modern day employee/employer relationship.

and was necessary for ancient civilizations to survive due to their lack of technology.

Here comes the apologist spin. You know slavery is wrong yet you have to come to grips with it somehow because your god not only allowed it, but condoned it.

The Bible over and over again stresses the importance of treating every human being equally

Equal you say?

You may also purchase the children of such resident foreigners, including those who have been born in your land. You may treat them as your property, passing them on to your children as a permanent inheritance. You may treat your slaves like this, but the people of Israel, your relatives, must never be treated this way.

God is always playing favorites.