I would LOVE to learn more about how you’re setting the AFX3/Apollo/DAW connections up...
My gear is a bit antiquated because it still works well. I have an Apollo Quad hooked to an old 2009 iMac. It has 32G RAM and a 10TB drive. I use Logic X and my Axe III is simply plugged in with one S/PDIF cable to the Apollo. On the UA monitoring software (Console) I have the S/PDIF channel as well as one stereo channel V1/V2 from Logic and another stereo channel V3/V4 from the computer itself.
I can then blend my Axe with Youtube jams or practicing with backing track software I use (Showbuddy) as well as blend the Axe with Logic without impacting the record level.
I rarely use the Unison feature and didn’t buy the UA for that. I do use it when tracking bass but I use an LA610 hardware unit for vocals. To me the beauty is in the Console monitoring software, easy connection. It is true some of these plugs are stellar. Fairchild 670 on drums, or a DBX 160 on base, the Capitol Reverb on vocals are worth the price of admission. I can’t say it’s value for guitar only but I do mixing and mastering and it’s a nice rig.
My downsides are I am stuck on old upgrades. Stuck on 9.14 on UAD, 10.13.6 on the iMac and 10.4.8 on Logic. I’m trying to ride this pony as long as I can because it will cost me probably 5K to 6K replacing my setup but I fear the time is near as I get more and more ‘your’e out of date’ messages.
Setting up both systems as aggregate devices is pretty straightforward. We jam a lot live into Logic via X32 Rack Mixer and experimenting with aggregate devices allowed us to track dry, wet, DI at the same time. There have been times we pulled a studio worthy track but it was saturated with either too much or wrong type FX. Not any more.
I can acquire a card replacement for the Quad I use to convert to Thunderbolt at a pretty reasonable price and get a bit more use out of it. Looking into computer replacement now. I have a bad habit of upgrade-itis and by the time I’m done configuring = $$$$.