That s this point which i really don t know how to...like the A16 has the mini jack output channel, so should it split physically as minijack to L/R RCA with one RCA to the input of the active speaker and the other one to the input (LFE) of the Sub? and to measure the Sub only by itself, should i just go for the A16 minijack output to L/R line input of the Sub?
No. Each mini jack output outputs 2 channels. So if for example you have a minijack to L/R male RCA connected to the A16 jack output labeled 1-2 then channel 1 is going to the left RCA plug, and channel 2 is going to the right RCA plug of that cable.
So if you want to measure channel 1 (and which virtual speaker that is is defined in the selected PRIR soundroom, that is either PRIR soundroom 1 or PRIR soundroom 2, the selection between the 2 is done somewhere in the APPS->PRIR measurement menu's) with an active speaker and an active subwoofer you have to split the signal going to that male RCA left plug. For example with another cable that splits one RCA female to 2 RCA male plugs. One going to the active speaker and one to the subwoofer.
If that channel 1 was assigned to be the subwoofer (in the selected PRIR soundroom) and you want to measure the subwoofer alone then you connect only the left male RCA of your jack to RCA cable to the subwoofer.
Another matter is whether that subwoofer has 1 or 2 RCA inputs, and whether it would be better to use both or no problem to use 1.
If you have 2 active speakers and a subwoofer with 2 RCA inputs then for example you can split the left RCA (channel 1) to one of the active speakers and one of the subwoofer inputs, and split the right RCA (channel 2) to the other active speaker and the other subwoofer input.
Hope you get the idea now, it would be difficult for me to explain all possible variations.
If for example you want to create a PRIR with 2 virtual loudspeakers, using only one active loudspeaker and an active subwoofer: you first connect the active speaker and sub to output channel 1 as described earlier, select only speaker 1 in the speaker select menu, measure the speaker, (after that press "back" not "enter"!), then connect the active speaker and sub to output channel 2 (as described but using the right RCA from the jack to RCA cable), only select speaker 2 in the speaker select menu, measure again, now press "enter" not "back"! and the PRIR containing 2 virtual speakers is created.
Again I hope you get the idea, again I didn't mention all the details but a few important ones!