I dont plan to go with m10 its junk, marantz overpriced junk as well these models 30 -40 so i am looking for nad c298 power amp,
of course manuals can be obtained online for most things.
But your problem is, you can buy the power amp but are ruling out just about every option for a decent DAC/pre in your price range to go with it.
The "overpriced junk" isn't overpriced if you can't do better for the same money, is it?
And that's before we are certain that the DAC/pre you get has matching output to the power amp input, and sufficient gain.
Clearly, though, you do have dealers where you are that stock these components. So find your local NAD C298 dealer and see what they have and can recommend.
It's just a shame that the matching NAD C658 actually IS a piece of junk.
Perhaps you should just consider importing the low price DAC/pre combos in the blue end of the SINAD list here, and forget the tax claim. Just make sure the preamp output properly matches the C298 input for voltage, impedance and gain. Fortunately, the C298 is well designed and has variable gain with a reasonable maximum: but your preamp will have to have a few dB of gain.
Personally, I'd recommend the dealer approach. Just don't let them sell you fancy cables!