Both domains are very important. I suggest that you use both of them in different ways.

If you believe that your empiric spirit domain is a "company" that you would like to support in social media and in articles, etc., for years to come, support it on its own domain separately from your personal domain.

However, I surmise that your personal domain is where you will (and, in my opinion, should) be driving up your social media presence and content. So, I recommend that you direct all book traffic there.

So, create a subdomain for your site, or a subfolder, and "point" your book domain to that subfolder. Write about the book in your social media and blog, and all traffic will come where you want it to ultimately come - your website.

It's important to maintain a website for the success of your book - for informational purposes, and to show people where to purchase the book. But it is important that you use social media like a pro, and become a guest blogging expert and frequent guest on radio programs... Those things matter much more. Direct all traffic where you want using bitly links, and track what is most effective.

Good luck! Enjoy the journey :)