Got my Helix yesterday, immediately updated to version 1.02.2. During setup, configuration and patch editing I had the following issues.
Here's an update on the issues below based on OS X 10.11.1 releases Oct 21.
1. USB Audio/MIDI does not work properly on MacBook Pro 2015 Retina 15" (has USB3 ports) with El Capitan. Behavior is different on an older MacBook Pro running Yosemite. There are perhaps a set of related issues:
USB audio now seems quite stable in El Capitan 10.11.1 for HD500X and Helix. Interesting that this was an OS X bug, not Line6.
1.a. The Helix audio device shows up as two devices in El Capitan Audi/MIDI Setup. One has 0 inputs and 8 outputs, the other 8 outputs and 0 inputs. The inputs and outputs work, buy this does not appear to be correct. On Yosemite, there is one Helix Audio device with 8 inputs and 8 outputs as expected.
Helix now shows up as a single device with 8 inputs and 8 outputs as expected.
1.b. The Helix App does not reliably connect or stay connected on El Capitan. It is getting USB timeouts and either shows Disconnected or service not available. Others have reported this. Works fine in Yosemite, never disconnected once with the App up and used for hours.
Helix app connects reliably and stays connected on 10.11.1 - but... saving a set list hangs the Helix app. And now I'm getting the black screen when turning on Helix. Not sure these are related but they happened around the same time.
2. Changing the Helix audio sample rate from 48kHz to 44.1kHz or any other value has no effect in El Capitan or Yosemite. The Audio device still shows 48kHz, as do apps like S-Gear that detect the sample rate. The sample rate dropdown list for the AudioMIDI Setup Helix device only provides 48000, there is no other selection regardless of how the sample rate is set in Helix.
The sample rate still does not change when updated on Helix, its fixed at 48000Hz, and the Audio/MIDI Setup on Mac OS X only shows 48000.
3. Helix MIDI over USB does not work. I select MIDI over USB in the Helix global parameters, but no MIDI messages are received in El Capitan or Yosemite. The Helix MIDI devices shows up in Audio/MIDI Setup, and MIDI from the MIDI DIN input and output also work correctly.
The USB MIDI is now working ok.
4. I agree with others that the joystick rotation is too sensitive and results in too many unintended model changes that result in lost parameter settings. This should be tuned to be less sensitive so that selecting blocks does not result in model changes. It is not reasonable to have to carefully handle the joystick while bending down to reach a device on the floor while you have a guitar in your hands, in a live setting.
5. Looper footswitches (record, play/stop, undo, etc.) don't send any MIDI messages like they did on HD500X. These are needed to allow Helix to control a computer looper in applications like MainStage so that you don't have to loose the ability to control stomp blocks. The looper block acts like a mode switch to temporarily reassign the footswitch functions. This needs to change the MIDI message too. It would be best if these messages could be configured - but fixed messages, as in the HD500X are OK. Helix receives MIDI to control the Looper, but the Looper doesn't send these MIDI messages like it does with HD500X.
6. TAP scribble strip light went out and no longer works. That's probably not a software problem, but possibly. Factory reset didn't fix it.