Two subs will sound substantially better than one because you won't be able to localize where the bass is coming from.
Adding a 2nd Sub to a 2 Channel System
I'm using a JL Audio E-110 sub in my system with Lawrence Violin SE stand mounted speakers. Since my Primaluna Integrated amp uses a dedicated mono RCA output, the speakers run full range and the sub is crossed over at 45hz per my Lawrence dealer's recommendation. Based on this configuration, is there any advantages of a 2nd sub by adding a Y connector and splitting the signal to 2 subs?