I don't have a 3.5 jack.
Here is mine

 

I don't have a 3.5 jack.

Then what is plugged into the headphone socket?

You just need a headphone jack to RCA output cable.

 

Then what is plugged into the headphone socket?

That's a power input

 

That's a power input

Then that does not appear to be the same as the device you referenced in Post #1.

 

You are indeed correct. I grabbed a screen shot of what I thought I had.

 

So your choices seem to be:

• Try to increase the gain of your audio amp (Post #11).
• Add an audio preamp to the device you have.
• Change to a Bluetooth converter.
• Try a different Toslink converter.

The first two have a high chance of working.
The bottom two are unknown (unless you find one that has the output voltage specified).

 

Can't say, since neither specifies the output voltage level.

As suggested by others, I'd try using the headphone jack output on the one you have to see how that works, before doing anything else.

I totally agree with "C", which is that the output voltage is never mentioned. Thus the entire product is suspect.
In addition, the price for that amplified version that has a headphone output is about a third of the price for mine from "Micro Center". Reading the advertising convinced me that I do not want to deal with that seller.

As for connecting to the headphone jack, my smart TV does not have a headphone jack, and on my other one plugging in disconnects the speakers.

 

So you have tried every TV made, right? Sorry, but you missed at least one. I had a TV that worked that way. And it makes sense, you can then adjust your volume with your TV remote.

Not all, but probably about 20 TVs and about 10 integrated amplifiers. Every single one had much lower volume level. It probably has to do with the headroom in the digital format. I had to turn the volume up +10-20db compared to other inputs, but it was never too quiet. Just had to turn it up.

The point of TOSLINK output on TVs is to send multi-channel audio streams to a multi-channel amplifier. These optical or copper digital audio outputs on TVs can handle an array of different codecs, stereo, Dolby Digital, DTS, etc. The audio stream is coming directly from the source. I can't imagine there is any consumer level device out there that will unpack a multi-channel audio stream, turn the volume up, and then re-pack it again.

 

My receiver has individual gain adjustments to equalize sound levels per input for all sources, including TOSLINK multi-channel audio streams.

Denon receiver web settings interface:

+- 12dB adjustment per source including the two fiber and two coax TOSLINK inputs.

Most of the time today the audio source is via HDMI.

DISH NETWORK like to run their sound hot, so it's leveled down -7dB to match other sources.

 

A quick search found this for audio gain adjustments. Don't know if it will work with digital input levels

The TS already has a Toslink Digital to Analog output converter, so would be adjusting the analog gain of his Rega Mira audio amp.

 

Mike "A" is totally correct in post #28. There is no reasonable way to adjust the level on the digital side. The problem that the TS suffers is an inadequacy of their audio amplifier system. That might be able to be corrected IF and ONLY IF the TS is competent to access the inside of that system and replace the resistors that attenuate the analog audio input signal for that connection.
I caution all that such a modification is only for those with adequate understanding, skill, and resources.