Thanks for the rear panel pictures. That helps.
What you'll need is a Speaker Level to Line Level convertor.
Compared to Line level signals, speaker level is relatively high voltage and high current. Reading between the lines of your Denon's specs, you have around 20W/ch in to 8 Ohms to play with, and so it will be raising around 12-13V and delivering about 1.5 amps of current in to an 8 Ohm speaker at full volume.
Line level is nothing like that. There's maybe a couple of volts and virtually no current.
To bridge between those two worlds, something needs to be used to pull the voltage right down to line level rates. Also, since it's the speaker that draws current from the amp rather than the amp pushing current in to a speaker, then putting a very high Ohms load on the speaker outputs means that the current will be very low but there'll still be a little power to dissipate.
The problem with pulling down the levels like this is noise. A speaker level output will have some noise from the amp stage of your Denon. The noise will still be present when the signal is reduced. Feeding that noise along with the audio signal in to the line input of the CS TV5 which then amplifies it will make the signal noise more noticeable compared to a much cleaner standard line level signal. Good circuit design can help minimise this, but it'll never make a pure line level quality signal from a speaker level output.
There are High-level to Low-level convertors available off-the-shelf. However, most are designed for the car audio enthusiast market. They're not so fussy about noise because any engine- and road noise- swamps the signal noise. At home though, you'll hear what the car boys can't pick up. For that reason, try to avoid car audio products.
Some of these car audio products are easy to spot because they have something in the description, or there are connections with spade terminals and fly leads. Others are harder to identify.
Home audio devices include the Russound ADP-1.2 and Xantech SLLC1, but neither is readily available in the UK. However, the same result can be achieved with some simple components and a bit of DIY soldering.
