Yes, Apple made a "safety feature" that requires you to have XCODE 8 BETA installed and running before you can install any BETA IPSW NO MATTER if modified (CFW) or untouched (original).
Not having XCODE 8 BETA installed was widely reported on all websites to make iTUNES to trigger Error 14 which means the build is corrupted.
==Why Apple Did That?==
Good question. iOS 10 BETA 1 is NOT INTENDED for Public Usage, but for Apple Developers which are being considered to have XCODE 8 BETA installed (to be able to create Apps for iOS 10 and macOS Sierra). It has a point and is completely logic. This build is not a public release, that's why you can barely find these IPSWS.
With the arrival of iOS 10 BETA 1, Apple kinda changed the rules. If Apple Developer Portal was partially available without any paid account on prior versions, with iOS 10's BETA you can no longer see anything from it without having a Paid Account.
==How this affect you?==
Well, it does not affect you. You can still install BETAS with provisioning profiles and XCODE 8 BETA for which I can't put any links due to legal matters, but PLEASE don't ask for Windows Methods. Windows has nothing to do with installation of iOS BETAs. iTunes alone, without XCODE 8 only allows the installation of RELEASE software which means PUBLIC not BETA.
If you want to install BETAS you need a MAC or at last OS X in Virtual BOX.
==What can you do?==
Well, if you don't have a MAC forget the idea of iOS 10 BETA installation via IPSW. You can't run XCODE on Windows, that's simply how it is. You need to use iOS 9.3.2 until iOS 10 is Fully RELEASED.
Don't blame me, blame Apple, I am not the one who decides what works with Windows and what does not.
==Interesting resources about the problem==
As you can see almost everybody had Error 14 during iOS 10 BETA installation, but Apple has a notice about XCODE on Apple Support page.