Hey Guys!
It seems there is some confusion in this thread. Let's see if I can help clear things up.
The iRig HD 1 (The original) did not include any output options. This allowed the iOS headphone port and speakers to be used with the iRig HD 1.
http://www.ikmultimedia.com/products/irighd/*This will also be the case for the iRig Pro (Original) as this does not include any output options.
http://www.ikmultimedia.com/irigpro/The iRig HD 2 now includes output options, both a dedicated amplifier output, and a headphone port. Due to this, the iOS headphone port and built-in speakers will be disabled. This is by iOS design and cannot be changed at this time.
http://www.ikmultimedia.com/products/irighd2/*This is also the case with the newer iRig Pro I/O as this offers a headphone port.
http://www.ikmultimedia.com/irigproio/If you have troubles getting your iOS headphone port or iOS built-in speakers to playback any signal with the iRig HD 1 (The original) or the iRig Pro (Original). Please contact our Technical Support team for assistance here.
http://www.ikmultimedia.com/contact-support/If you have the iRig HD 2 or the iRig Pro I/O. Do note, this is normal behavior here due to iOS design. Please use headphones or external speakers with these units.