i have a onkyotx-nr616 can i hook up 2 sub woofers to it
Yes, you can connect one, two or more subwoofers, but they must be identical (I guess you are trying to give visual symmetry to your setup) and of an active type (your system can only output a line subwoofer signal, so you must have an amplifier and a subwoofer). However, I suggest you to use a larger subwoofer (it doesn't matter where you put the subwoofer, the low frequency sounds propagates all around the enclosure):
The use of multiple subwoofers will give you smoother bass if you can spread them around the room. This creates different standing waves for each sub in the room so the room will have less effect on the bass than you would get with one larger subwoofer. I would still keep them toward that front of the room. Closer to the TV than to you.