So how did you use the calculator to get that particularly?
Assuming it's a reasonable calculatation, not quite reaching THX reference movie volume would be okay with you (peaks from speakers 105dB) ? Reasons for a power amp..... Allowance for cleaner peaks / more overhead when playing at higher volume perhaps, or being able to be used with a wide variety of speakers / rooms without worrying about power as much, driving lower sensitivity / impedance speakers (or "difficult to drive" speakers), or just because you want to
....a variety of reasons.
My particular take is in a large room at higher volumes it can be a nice thing, did it for years and I do generally buy avrs with pre-outs simply to have the option. In the last few years have deliberately backed off on volume (-20 dB generally, maybe once in a while some music a bit louder) and have more sensitive speakers in my main system than I used to....but adding a power amp at these levels yielded no audible difference to me vs. using my avr alone (but have some extra amps so I hooked 'em up anyways....LOL). That's where I'm 14 ft from the mains, 7ch system, 32 x 15 ft room, my avr is similar power to yours, perhaps a bit more powerful (150wpc).
Takes a doubling of power to gain 3dB spl so if you do go external amp go fairly big, I'd aim at that 250-300 wpc range. Didn't look at your speaker spec but I've noticed some Dynaudios I've read about are somewhat low impedance, and wouldn't be surprised if the MA's are also; but not familiar with the brands generally (never saw them in my visiting stereo stores days). Bookshelves tend to be low on the sensitivity side, too. You might still be a candidate but I'd still use the avr alone; it's easy enough to add amps later....
