I did these test years back using many world class converters. When mixing with outboard, I eventually moved towards two DAWs and never looked back. I learned a great deal from it. I avoided round trip processing and talked about this. Long story... Once ITB, stay ITB.
I remember in DP7, we would have to add a "dummy" effect on parallel channels because otherwise the delay compensation wouldn't work properly, and you'd get phasing.
I love itb, but i realize more and more how little i know about whats going on under the hood. Lol one sample library loads to ram, the other streams off the ssd, one loads across multiple cores, the other single core only.
I think my naive "throw paint at the canvass" methods of yesteryear, exposed many flaws in my knowledge and the programs, that contributed to me chasing my tail.