wouah that is making a lot of extra work!
Simply speaking, is mini box pico psu @160w using their mini power adapter is completely compatible to s4 mini? Even internal wire length to external power brick?
Same question pour hdplex 250w with voodoo 350w in terms of external plug to power brick...
Great question. The answer is DEPENDS ON YOUR MOTHERBOARD and where it puts the 24 pin. Motherboard manufacturers for Intel have started being more consistent and putting the 24 pin opposite the I/O side of the board biased toward the PCIE slot, where it will not require any lengthening. However, I have two boards (AMD and a BIOSTAR Intel) that put the 24 pin as far away as possible from the S4's power port. They require lengthening.
You don't have to be fancy at all if you want to extend it to make things easy--a couple butt connectors are fine for those two power cables (the black and white ones). Soldering is always better, but not necessary. I can include lengths of wire (and butt connectors) so you don't need to source anything if you just ask with your order.
The HDPLEX's wires are ridiculously long and you won't have any reach issues.