Alright guys,
I was able to accomplish this round trip setup. And the more I get into it the more I understand that my previous questions from my most current post where not too reasonable...
Neither did I know that Logic would create a ping/peak signal on its own nor that the different kind of Kemper-Amp-sims you'd use would cause different latencies, regardless if you're using FX or not.
So, I just put the I/O plug-in on a Logic channel aux/bus and used the usb connection to the Kemper to create a round trip on input/output channels 3-4, having to choose the Profiler as input and output in the preferences first of course. The spdif I usually use as the connection from the Kemper into my DAW and wanted to test in the first place wouldn't work, since once you are using reamping in Kemper to send back the stereo or stack signal via USB it would not let you take spdif as an Input source anymore.
Anyway, this worked eventually at least with USB, and it all took me a while to figure it out.
So, then I ping-ed and it eventually showed me a latency offset.
Depending on which buffer size I would choose in the preferences, I'd get latency offsets of 1434 samples (1024 samples buffer size) or 343 (for a 32 samples buffer size) - both regarding the same Kemper profile of a distortion sound. So, if I do the math, that leaves me with around 7,7 ms (343/44100 x 1000) for the smaller value, which seems to be in the ballpark of what I was expecting. I usually have the buffer size on 1024 samples for mixing, though.
However, what actually is it about the buffer size in this scenario? I would have to subtract the buffer size samples from the latency offset to do it accurately, cause I only care about the offset between the amp and DI signal within the Kemper, correct? So, for the smaller value, it would be 311 samples latency offset, right?
OK, but even if I do all this (with having set the Kemper to constant latency) and delay the DI track region by this value (converting it to ticks), the phasing varies a lot depending again on which amp sim I use on the DI in logic. I mean, of course, I would suppose so it differs, cause different amp sims have different algorithms, but I would have thought that this is what the latency compensation in Logic is for, and that it wouldn't differ so much.
So, long story short: Once I know the latency offset of the Kemper for a certain sound, is there a smart way to have it all in phase in Logic with different Logic-internal amp sims? Is it - again - about the buffer size? Am I not getting something here completely? Aside from the latency while recording, buffer size doesn't affect the actual latency of the recording itself, right? Sorry, for being such a greenhorn, I just want to exclude any potential failures...