I have a an Omega single driver speaker ( super 3) set up with a superzen SET amp in my bedroom . Late night i usually lower the volume and some of the low frequency suffers . I am thinking about adding an 8 " sealed subwoofer . My question is what would be the best way to connect the sub to the superzen amp ?

Unless you want to invest in a preamp I suggest you select a sub with "Speaker Level" inputs. Connect a second set of speaker cables from your amps Left / Right speaker outputs to the Speaker Level input connections on the sub. I use inexpensive Cat 5 network cable for this connection with very good results in my system.

If you really want to improve lower volume listening then I suggest a Mid Bass Module over the Sub only approach. You can get more info here:

https://www.decware.com/cgi-bin/yabb22/YaBB.pl?num=1360355711/0#0