More than anything I'm trying to show you a system that has flexibility and the ability to upgrade.
Going with an outboard phono stage does not make things more complicated. It creates more options and flexibility. Not complicate things.
If you really like the Onkyo then go with it. Its a good amp. Just not what I would have chosen.
But please go listen to more speakers than the Deft Tech's. This is what will ultimately determine your systems sound.