MixPad  V1.9 will require firmware V1.9.

Firmware V1.9 requires the DSP RackExtra Two card to run on Modular iLive iDR10 and iDR0 Mixracks

There is a potential issue with the lack of a downgrade path from the Apple App Store.
For example; take the scenario you accidentally hit “update all” in your iOS App Store, before you receive your new DSP hardware.
This would render the host iPad unable to connect V1.9 MixPad to your V1.8 firmware, and unable to update your system firmware before the DSP card arrives.

The best advice, in this case, is therefore to only upgrade MixPad to V1.9 after delivery of your new DSP card.
To avoid the situation described above, the only available workaround requires the MixPad user to have kept a backup of their existing V1.8 MixPad application file (ipa), before the release of V1.9 MixPad.