I have never found a go-to book for arrangers. There's David Baker's Arranging and Composing for the Small Ensemble, which is the one I assume you have already found, and also the vintage Music arranging and orchestration by John Cacavas, which has some great tips and examples from the pre-digital age.

I have looked at Modern arranging technique: A comprehensive approach to arranging and orchestration for the contemporary stage band, dance band, and studio orchestra by Gordon Delamont, and The Professional Arranger/Composer by Russell Garcia. If you want to study jazz arrangements, besides Baker's book, you could take a look at what Leslie Sabina has written.

I also know of, but have not seen, Music Composition and Arranging by Samuel Walter and the Mel Bay Basic Concepts of Arranging and Orchestrating Music, which, by all accounts, is a little elementary.

[="http://www.berkleepress.com/catalog/category-browse?category_id=7"]Berklee Press[/]="http://www.berkleep…"]Berklee Press[/] has a section on writing and arranging, including Arranging For Large Jazz Ensemble by Ken Pullig and Dick Lowell, which I don't know, but looks to be an authoritative work on that topic.

[[url=http://="http://roydmagnuson…"]Here[/]="http://roydmagnuson…"]Here[/] is a bibliography compiled by Roy D. Magnuson on orchestration and arranging.

This is not a long list, but I hope it helps. What it shows is that there is a niche for an up-to-date book on professional arranging in the digital age. If I had the time....