We have contacted Apple about this. The issue is specific to Logic 10.6, older versions work fine with the multichannel output of Pianoteq.

Hi, i'm on Logic Pro 10.5 and i have the same issue with Pianoteq 7 and Pianoteq 8 (it was the same thing in the older versions). None is working on multi output. What could i do to to change that please?

validating Audio Unit Pianoteq 7 by Modartt:

    AU Validation Tool
    Version: 1.7.0
    Copyright 2003-2019, Apple Inc. All Rights Reserved.
    Specify -h (-help) for command options

--------------------------------------------------
VALIDATING AUDIO UNIT: 'aumu' - 'Pt7q' - 'Mdrt'
--------------------------------------------------
Manufacturer String: Modartt
AudioUnit Name: Pianoteq 7
Component Version: 7.1.0 (0x70100)

* * PASS
--------------------------------------------------
TESTING OPEN TIMES:
COLD:
Time to open AudioUnit:         451.225 ms
WARM:
Time to open AudioUnit:         69.688  ms
FIRST TIME:
Time for initialization:        0.213 ms

* * PASS
--------------------------------------------------
VERIFYING DEFAULT SCOPE FORMATS:
Input Scope Bus Configuration:
Default Bus Count:0

Output Scope Bus Configuration:
Default Bus Count:1
    Bus Name: Output
    Default Format: AudioStreamBasicDescription:  2 ch,  44100 Hz, 'lpcm' (0x00000029) 32-bit little-endian float, deinterleaved

* * PASS
--------------------------------------------------
VERIFYING REQUIRED PROPERTIES:

* * PASS
--------------------------------------------------
VERIFYING RECOMMENDED PROPERTIES:
  VERIFYING PROPERTY: Latency
    PASS

* * PASS
--------------------------------------------------
VERIFYING OPTIONAL PROPERTIES:
  VERIFYING PROPERTY Tail Time
    PASS
  VERIFYING PROPERTY Bypass Effect
    PASS

* * PASS
--------------------------------------------------
VERIFYING SPECIAL PROPERTIES:

VERIFYING CUSTOM UI
Cocoa Views Available: 1
  JUCE_AUCocoaViewClass_bf43d764ccf41a4d
    PASS

HAS FACTORY PRESETS

VERIFYING CLASS INFO
    PASS

TESTING HOST CALLBACKS
    PASS

* * PASS
--------------------------------------------------
PUBLISHED PARAMETER INFO:

# # # 205 Global Scope Parameters:
WARNING: retrievedValue = 0.551162 (was 0.551162), Parameter did not retain default value when set
WARNING: retrievedValue = 0.500000 (was 0.500000), Parameter did not retain default value when set
WARNING: retrievedValue = 0.500000 (was 0.500000), Parameter did not retain default value when set
WARNING: retrievedValue = 0.000000 (was 1.000000), Parameter did not retain maximum value when set
WARNING: retrievedValue = 0.000000 (was 1.000000), Parameter did not retain maximum value when set
WARNING: retrievedValue = 0.000000 (was 1.000000), Parameter did not retain maximum value when set
WARNING: retrievedValue = 0.500000 (was 0.500000), Parameter did not retain default value when set
WARNING: retrievedValue = 0.424742 (was 0.424742), Parameter did not retain default value when set
WARNING: retrievedValue = 0.500000 (was 0.500000), Parameter did not retain default value when set
WARNING: retrievedValue = 0.741444 (was 0.741444), Parameter did not retain default value when set
WARNING: retrievedValue = 0.597500 (was 0.597500), Parameter did not retain default value when set

* * PASS
--------------------------------------------------
FORMAT TESTS:

Reported Channel Capabilities (explicit):
      [0, 1]  [0, 2]  [0, 3]  [0, 4]  [0, 5]  [0, -5] 

No Input, Output Chans:
0-1   0-2   0-4   0-5   0-6   0-7   0-8
X     X     X     X                       

WARNING: Source AU supports multi-channel output but does not provide a channel layout

* * PASS
--------------------------------------------------
RENDER TESTS:

Output Format: AudioStreamBasicDescription:  2 ch,  44100 Hz, 'lpcm' (0x00000029) 32-bit little-endian float, deinterleaved
Render Test at 512 frames
Slicing Render Test at 64 frames
  PASS

Render Test at 64 frames, sample rate: 22050 Hz
Render Test at 137 frames, sample rate: 96000 Hz
Render Test at 4096 frames, sample rate: 48000 Hz
Render Test at 4096 frames, sample rate: 192000 Hz
Render Test at 4096 frames, sample rate: 11025 Hz
Render Test at 512 frames, sample rate: 44100 Hz
  PASS

1 Channel Test:
Render Test at 512 frames
  PASS

Bad Max Frames - Render should fail
  PASS

Checking parameter setting
Using AudioUnitSetParameter
Using AudioUnitScheduleParameter
  PASS

Checking ramped parameter scheduling
  PASS

Test MIDI
  PASS

* * PASS
--------------------------------------------------
AU VALIDATION SUCCEEDED.
--------------------------------------------------

validation result: successfully validated

updating properties of AU Pianoteq 7 by Modartt…

what am I trying to do?

I want to load Pianoteq 7.1 as a 5 output multi-output plugin. It's fine with me if it's 16x mono, or 25x mono - I know what to do with unused outputs... but nothing other than stereo or mono work. As standalone, multiple outputs do work.

this is macOS 11 (latest) with Logic (latest) using Pianoteq (latest)