Power Amp Question

@bop333 

     IF your question is how to use your NAD integrated as a preamp only: there should be two links (rectangular, black plastic covered) between the C356's rear PRE OUT 2 and MAIN IN RCA jacks.

     Remove those and simply plug a pair of interconnects, between the PRE OUT 2 jacks and your new amp's input jacks.

     If your desire is to add a second amp: use interconnects from PRE OUT 1, to that amp and leave the PRE OUT 2/MAIN IN links alone.

@bop333 -

     btw: Are you dissatisfied with your system's SPL output, with all sources, or- only with your analog setup?

     I've been trying to find the voltage output for your AT MC cartridge, but: guess that's a company secret.

     The output levels of many MC carts are too low for some systems.    In those instances: additional gain devices (ie: a transformer or higher gain phono pre) may be needed.

     Just thinking your system may not have enough gain, to step up the cart's output to satisfying levels, as a possibility.

@bop333 -

     Supposedly: your current speakers are fairly sensitive, at 92 dB/1W/1M.   

     Many SS amps will safely double their 8 Ohm output wattage ratings, into a 4 Ohm (nominal) load, which your speakers will present.

     According to the specs: your NAD doesn't, staying at 80 WPC, into both 8 and 4 Ohms.

     You might try a 200 WPC @8 Ohm amp, that you've confirmed will safely handle 4 Ohms (preferably: double it's output), with your Triads and see if they satisfy, prior to making any other leaps.      

                        If not: more efficient speakers may be your ticket. 

@bop333 -

                       Have fun and happy listening, George!