Saturday - Weekend! All garden work done and found some time to tinker with this bad boy some more.
Actually wired and fired it all up and put that old empty SKB 8U Shockmount monster to some good use while doing so...
Pic first:

I intentionally left some space between the units to get some good air circulation in there and this way I can skip the need to put an extra rack fan array in (the Carvin tends to produce some temperature and both preamps have vented top and bottom cover plates).
Signal flow/routing as follows:
Guitar (I might add a Line6 Relay G75 in there later) > Access > Access Preamp Insert Send > MP-1 > MP-1 Out > Access Preamp Insert Return > Access Serial Loop Send > Roland GP-100 In > Roland GP-100 Out > Access Serial Loop Return > Access Out > Carvin Tube100 In (Mono) -> Carvin Tube100 Out A > Mesa Thiele with C90 /// -> Carvin Tube100 Out B > Mesa Halfback 2x12 with V30/C90
I only used the Serial Loop and skipped all that fancy parallel loop b and parallel loop c stuff for the time being.....
O.M.F.G.!!!!!! This thing sings AND rips!!! Both preamps by themselves sound stellar (the MP-1 is S.S./Noise/...and whatnot modded and refurbed in almost all parts of the signal path), but the MP-1 in the Access' Preamp Insert is out of this world. The Insert allows to make use of the Access' onboard Mid-Boost and Treble-Boost...AND you can further use the Access' EQ to shape the tone...how cool ist that?!?!!!!
I'll have to further dive into the Access' MIDI-Mapping since theres some changes programmed that affect all thats connected, but thats something for next week.
And I'll have to wait til both my fam and the neighbours are out so I can turn the poweramp's volume past noon

But for now....happy camper!!!