Hi,
My setup is as follows:
Desktop -> Nvidia HDMI Audio -> Sony Receiver -> TV
Desktop -> Logitech USB Headset (Model: H390)

In Settings -> Audio -> Interface I have the following set:

Internal Sound Card and Port: HDA Nvidia
Sound Presentation: Digital Surround 5.1 (HDMI) Output
Sound Output Port: HDMI / Display Port

In Settings -> Audio -> Voice

Voice Recording Device: Logitech USB Headset
Voice recording port: Microphone
[X] Use for voice output too

The first time that this configuration is set, it works properly. However, once Big Picture Mode is restarted, ALL audio goes out of the headset until the headset is disabled for a restart cycle. Please fix as this is very annoying; the main audio should be output as to how I have it set in the Interface settings.

Computer Information:
    Manufacturer:  Unknown
    Model:  Unknown
    Form Factor: Desktop
    No Touch Input Detected

Processor Information:
    CPU Vendor:  GenuineIntel
    CPU Family:  0x6
    CPU Model:  0x3a
    CPU Stepping:  0x9
    CPU Type:  0x0
    Speed:  4600 Mhz
    8 logical processors
    4 physical processors
    HyperThreading:  Supported
    FCMOV:  Supported
    SSE2:  Supported
    SSE3:  Supported
    SSSE3:  Supported
    SSE4a:  Unsupported
    SSE41:  Supported
    SSE42:  Supported
    AES:  Supported
    AVX:  Supported
    CMPXCHG16B:  Supported
    LAHF/SAHF:  Supported
    PrefetchW:  Unsupported

Network Information:
    Network Speed:  

Operating System Version:
    Linux Mint 17.3 Rosa (64 bit)
    Kernel Name:  Linux
    Kernel Version:  4.4.0-18-generic
    X Server Vendor:  The X.Org Foundation
    X Server Release:  11701000
    X Window Manager:  Mutter (Muffin)
    Steam Runtime Version:  steam-runtime-release_2016-02-23

Video Card:
    Driver:  NVIDIA Corporation GeForce GTX 980 Ti/PCIe/SSE2

    Driver Version:  4.5.0 NVIDIA 364.15
    OpenGL Version: 4.5
    Desktop Color Depth: 24 bits per pixel
    Monitor Refresh Rate: 60 Hz
    VendorID:  0x10de
    DeviceID:  0x17c8
    Number of Monitors:  1
    Number of Logical Video Cards:  1
    Primary Display Resolution:  1920 x 1080
    Desktop Resolution: 1920 x 1080
    Primary Display Size: 62.99" x 35.43"  (72.24" diag)
                                            160.0cm x 90.0cm  (183.5cm diag)
    Primary Bus: PCI Express 16x
    Primary VRAM: 6144 MB
    Supported MSAA Modes:  2x 4x 8x 16x 

Sound card:
    Audio device: Realtek ALC898

Memory:
    RAM:  32138 Mb

Miscellaneous:
    UI Language:  English
    LANG:  en_CA.UTF-8
    Microphone:  Not set
    Total Hard Disk Space Available:  938581 Mb
    Largest Free Hard Disk Block:  453679 Mb
    VR Headset: None detected