Поддерживает ли AV-ресивер Pioneer SC-LX704 функцию HDMI Ethernet Channel?

по идее это должно быть написано у вас в инструкции к ресиверу.... смотрели ?

В инструкции среди технических данных о поддержки данной функции ни слова

Compatible functions
HDMI (High Definition Multimedia Interface) is a digital interface standard for
connecting TVs, projectors, Blu-ray Disc/DVD players, digital tuners, and other
video components. Several separate video and audio cables have been required
to connect AV components so far. With HDMI, a single cable can transmit control
signals, digital video and digital audio (2-channel PCM, multichannel digital audio,
and multichannel PCM).
HDMI CEC function:
By connecting a device that complies with CEC (Consumer Electronics Control)
of the HDMI standard using an HDMI cable, a variety of linked operations
between devices are possible. This function enables various linking operations
with players, such as switching input selectors interlocking with a player,
adjusting the volume of this unit using the remote controller of a TV, and
automatically switching this unit to standby when the TV is turned off.
The unit is designed to link with products that comply with the CEC standard,
however, linked operation is not always guaranteed with all CEC devices.
For linked functions to work properly, do not connect CEC-compliant devices
exceeding the connectable number to the HDMI jack as shown below.
• Blu-ray Disc/DVD players: up to 3 units
• Blu-ray Disc/DVD recorders: up to 3 units
• Cable TV tuner, terrestrial digital tuner, and satellite broadcasting tuner: up to
4 units
Operation has been confirmed on the following devices: (As of January 2019)
Toshiba brand televisions; Sharp brand televisions; Toshiba brand players and
recorders; Sharp brand players and recorders (when used with a Sharp brand
television)
ARC (Audio Return Channel)/eARC (Enhanced Audio Return Channel):
The ARC function and eARC function transmit the audio signals of the TV via an
HDMI cable, and plays the audio of the TV on this unit. By connecting an ARCcompatible TV or eARC-compatible TV with a single HDMI cable, you can output
the audio and video from this unit to the TV, and also input the audio from the TV
to this unit.
• The eARC function is a newly added function for HDMI 2.1. This is an
expanded function from the existing ARC function, and is able to send audio
formats such as Dolby TrueHD and DTS-HD Master Audio that cannot be sent
with the ARC function, from an eARC-compatible TV to this unit.
– ARC-supported audio formats: PCM, Dolby Digital, Dolby Digital Plus, DTS
(DTS 96/24, DTS-ES, etc.), DTS-HD High Resolution Audio, IMAX DTS
– eARC-supported audio formats: PCM, Dolby Digital, Dolby Digital Plus,
DTS (DTS 96/24, DTS-ES, etc.), Dolby TrueHD, Dolby Atmos, DTS-HD
Master Audio, DTS:X, Multichannel PCM, DTS-HD High Resolution Audio,
IMAX DTS, IMAX DTS:X
HDMI Standby Through :
Even if this unit is in standby mode, the input signals from AV components can be
transmitted to the TV.
Deep Color :
By connecting devices supporting Deep Color, video signals input from the
devices can be reproduced on the TV with even more colors.
x.v.Color™ :
This technology reproduces even more realistic colors by expanding the color
gamut.
3D :
You can transmit 3D video signals from AV components to the TV.
4K :
This unit supports 4K (3840×2160p) and 4K SMPTE (4096×2160p) video signals.
Lip Sync :
This setting automatically corrects desynchronization between the video and
audio signals based on the information from the HDMI Lip Sync-compatible TV.
Copyright Protection:
The HDMI jack of this unit conforms to the Revision 1.4, Revision 2.2 and
Revision 2.3 standards of the HDCP (High-bandwidth Digital Content Protection),
a copy protection system for digital video signals. Other devices connected to the

Страница 218 руководства.

Но про поддержку данной функции ни слова

Даже интересно, зачем вам понадобилась эта поддержка? Вообще-то этому стандарту уже лет пятнадцать, и практически все современные устройства с HDMI её поддерживают по умолчанию.

Зачем понадобилось ? Да затем чтобы увязать в одну домашнюю сеть и ноутбук, который не является стационарным компьютером. И нужен в сети время от времени, когда лишь подключаю его в качестве HD Player. Ну и ещё большой плюс, не нужно вести дополнительный кабель, ведь всё в одном HDMI передается.

Я прямо таки сомниваюсь что все устройства поддерживают этот стандарт.

ну значит нет...