Hello, I was just lurking and thought I should chime in. A friend recommended the Gilreath book to me, and it's been great. If you're looking for a really thorough and modern text on orchestration, I really recommend The Study of Orchestration by Samuel Adler (amazon link). It is pricy unfortunately, so maybe a library near you will have it so you can see how you like it. Regardless, it's definitely my go-to reference for orchestration.