Preamp - 18 dB Gain too low?

An input sensitivity for an amp of 1v is quite normal as nearly every amp I've seen on the market has been .5v to 2v for max rated rated output (to clip/distort).
An input sensitivity of 4v is wrong/bad and I would call the amp broken or seriously badly designed.
You have a problem ask the manufacture to give you a fix to make the amp/s 1 to 2 volt input sensitivity, as the standard is.

Cheers George

Nguyen787
Here is a way out there thought on your problem. You say your running the amp on 115v mains? It is possible that this amp/s are set up for 220-240v mains operation, this could? drop your gain/input sensitivity.

Cheers George

Another thought, your Oppo cdp has a remote volume control, is it at full output level? As it may default to 1v or less when powered up and you need to bring it up on the remote to full 2v output.

Cheers George

More on the Oppo's stereo only output, are you getting the siganl from the FL and FR outputs on the back to the Lightspeed?

Also taken from the manual are you setup it the programing for this way.
"4. Output Volume: Allows you to enable or disable the analog volume controls (also known as Variable
Audio). The available options are:
�� Variable – Enables the analog volume control. Use the VOL+/- buttons on the remote to
increase/decrease the analog audio output level (the maximum is 100).
�� Fixed – Disables the analog volume control. The VOL+/- buttons on the remote will no
longer affect the analog audio output, and the volume level is fixed to 100."

And then this also
"For the stereo outputs, if the audio system you are connecting to does not have surround speakers,
set the Down Mix option in the Setup Menu to Stereo. If the audio system has surround speakers
and Dolby Pro Logic or other surround audio decoding capabilities, set the down mix mode to “LT/RT”.
(For more information, refer to “Down Mix Mode” on page 68)."

Cheers George

Checked and corrected Oppo setting per suggestions, do not see any different on sound level. Volume --> fixed at 100%.

George raised an interesting concern - main voltage. The amp power outlet plug written "115 V, 50/60 Hz" seems OK for US AC electricity. I am wondering Shuguang started out design as for 230 V and made shortcut to convert to 115 V for North America market, compromised the amp voltage? I really don't know, just speculating. I did send my question to Grant Fidelity about the spect mismatch, but have not heard back from them yet.