Power Amp Question

 Speakers 100 - 450W - 4 ohm and the C356 80 watts is too little. I am not sure.

200?

Depends on how loud you listen.

This little monster should do ya.

That's as much as I would spend before getting a better pre.

@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 -

     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.

Why do you believe you need more power? (maybe you do, its just that there is no evidence or explanation here......)

You realize the relationship between power and volume is roughly logarithmic? so doubling it makes a very small difference.....

BTW if you do wish to upgrade i tend to agree that a better ovrall integrated would be a better choice - the signal is a chain and only as good as the weakest link after all.