Hi, I have GMX 2.1 and GMX 5.1

I would like to use the sub of GMX 2.1 as an additional sub for my GMX 5.1

is it possible??

can i just connect the sws link out of 1 sub to another sws link out to another sub??

I saw there is a similar post on this issue. Notice that the advice given is to connect sws link out of GMX 5.1 sub to the input of the console of GMX 2.1 using 1 male rca to 2 male rca.

However, my concern is that by doing so, the volume for each sub would be diferent as the volume of each sub is controlled using different console. Besides that by doing so, will it spoil the GMX 2.1 console and sub?? because instead of receiving full signal, the console only receive low frequency signal. 

Is there another method to connect these 2 sub so that i can control from the same consol?

 Thanks in advance