I'm with you on this, I use my Naim power amp with a direct 'line level' and volume controlled feed from an RME ADI-2 fs DAC. Despite other Naim owners ranting on about it needs 'the other half of the amp' to make it complete, i.e. the 'pre amp' I can see no reason why it should be necessary as I strongly suspect that the DAC is perfectly capable of driving the power amp to full power.
Quite what magic the matching Naim pre-amp is supposed to confer on matters is a mystery to me, unless it is designed to colour the sound.
Perhaps someone else knows better?