Can someone point me in the right direction? LP player / Preamp / Dragonfly Red...

Just to be clear, you cant input a TT into your iMac and use the Mac as your controller. This is only done when somebody wants to convert vinyl to an audio file by using a A/D converter.

You need a phonostage that would plug into the Sony (and there are many costing less than $350) or go with the Onkyo as you first suggested. It has an input for a TT and looks to be of much higher quality than the Sony.

They are 6 ohm, but really act more like a 4 ohm speaker with such a demanding load. The Onkyo specs only show a rating for 8 ohms. This usually means the amp doesn't have the power/current required to drive power hungry speakers like the Kappas. The 8.1 specs state a minimum of 50 watts.

What is the size of your room? And how did the Kappa's respond to your Sony?

TBH, in the world of amplifiers, that is a negligible difference in power between the 2 models.
  We've established that your Kappa's are basically a 4 ohm speaker, so we are not interested in the 8 ohm spec of 75 wpc. The speakers will be drawing higher current from the amp which relates to the 4 ohm spec. So the 9010 is rated at 60wpc and the 9050 is 65wpc,  they are basically the same power, even at 8 ohms. The difference between them is extra features on the 9050.

You're right, specs vary online.
This one has a rating of 70w into 4 ohms.
https://www.cnet.com/news/low-costhigh-performance-contender-onkyo-a-9010-integrated-amplifier/

I think the real issue is that the Kappa's are more demanding than a 4 ohm speaker. I dont see an impedance curve which would show how often there is a demand for high power/current.
  The Onkyo will certainly drive your speakers, but you may be missing out on detail and texture in the bass frequencies. It's possible that the speaker's demand during peaks and transients may push the amp into clipping, which is distortion.

With this combo you are at the very minimum of what the speakers demand. Have you looked at the next model up the ladder?, I forget the model number.

The Power Rating of the 8.1 is 40 to 300 watts RMS. That is a wide range and it would be to your benefit to move up to higher power and not be near the recommended minimum.

Suggest you look for a used integrated in the classified section or on US Audio mart dot com.