Connect Aurender A15 directly to Mac tube power amp

Wondering if anyone has had experience connecting Aurender A15 directly to Mac MC275 or MC1502. Given that A15 has the DAC on board and it'll be my single source for some time, do I really need a pre-amp? I've borrowed MC275 with and w/o C49. With C49, I definitely have more volume to work with, the mid range is bit more prominent, the sound stage maybe tiny bit wider, and maybe it's tiny bit more quiet. That's pretty much it - is it worth extra $5K, or I'm missing some fundamentals?... I'd rather get only MC1502 and have the extra power. 

I'm upgrading from my old SS Nakamichi PA-7 that is currently connected directly to A15 with plenty of power. Speakers are SF Sonetto VIII.