The dB and % is telling you how much the incoming signal is being reduced or increased. At 0, whatever is coming in is the same as what's going out (e.g. 1V in -> 1V out). At +6 it is double (e.g. 1V in -> 2V out).
The Technics SU-G700 says its line-level input sensitivity is 200mV, so when getting an input signal of 200mV it is outputting 70W into 8Ω. If your CD player is ~2V, or 2000mV, then -20dB / 0.1% would be 70W output, but if you're using the digital inputs I'm not sure but might guess -20dB is also 70W output when the digital signal has 0dBFS data.
Since the numbers are relative to the input signal, the -50 through +6 range isn't equal to a specific volume. If the input signal is someone barely whispering, you might have to turn it up close to +6dB to hear anything. While if the input signal is a pop song recorded at 0dBFS (i.e. max volume) then you probably need to turn it down to somewhere around -30dB or -40dB for normal listening volumes.
But how loud are you playing? The K9 speakers are listed with a sensitivity of 87dB. That should mean 1W at 1m distance is ~87dB and you can only listen to that for like an hour before risk of hearing damage. At 3m away, you only need like 10W for 87dB. And that's per speaker.
I think even if you have some hearing loss already, listening to loud music to compensate will only cause additional hearing loss and maybe also eventually tinnitus.
The Technics SU-G700 says its line-level input sensitivity is 200mV, so when getting an input signal of 200mV it is outputting 70W into 8Ω. If your CD player is ~2V, or 2000mV, then -20dB / 0.1% would be 70W output, but if you're using the digital inputs I'm not sure but might guess -20dB is also 70W output when the digital signal has 0dBFS data.
Since the numbers are relative to the input signal, the -50 through +6 range isn't equal to a specific volume. If the input signal is someone barely whispering, you might have to turn it up close to +6dB to hear anything. While if the input signal is a pop song recorded at 0dBFS (i.e. max volume) then you probably need to turn it down to somewhere around -30dB or -40dB for normal listening volumes.
But how loud are you playing? The K9 speakers are listed with a sensitivity of 87dB. That should mean 1W at 1m distance is ~87dB and you can only listen to that for like an hour before risk of hearing damage. At 3m away, you only need like 10W for 87dB. And that's per speaker.
I think even if you have some hearing loss already, listening to loud music to compensate will only cause additional hearing loss and maybe also eventually tinnitus.