Shuttles are barebones and already have their own proprietary mobo, PSU, cooling solution, etc. - you can't change to another.
While the XQpack uses all standard components including microATX mobos. Instead of the XQPack which includes a proprietary PSU (4.5" deep), get the Ultra MicroFly. The MicroFly is a bit longer and can more easily hold standard ATX PSUs (5.5" deep) - the other can hold PSUs of standard depth, but it can be a tight squeeze depending on the length of your optical drives (the short length optical drives are recommended for all of these). I generally recommend buying the case WITHOUT a PSU and put the PSU you need in there. I'm not sure if you can get the X-QPack w/o PSU, but I know you can with the u-Fly. I don't like having to recommend Ultra products, but here they've done it a bit better than the other two variants (the Chenming 118 is the third variant of the same case) .
I don't recommend the shoebox barebones like the Shuttle as they are generally not upgradeable except thru whatever Shuttle might offer to do so.
.bh.
