HeartKeys I’m using the following:
M-Audio Keystation 88. Terrible action but weights only 13 pounds, and powered by USB. And hey it’s 88 keys.
NewQ USB hub to connect my earphones and keyboard into the iPad.
iPad loaded with Pianoteq.
Shure SE846 earphones.
My traveling practice keyboard setup is based on the same principles, but I have a Swissonic keyboard, Pianoteq on my MacBook, and Soundblaster Play! 3 between the keyboard and the Mac. Not 88 though, but, that is okay.
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... feeling like the pianist on the Titanic ...