Using a sub with no sub out on my amp


I just bought a Rega IO amplifier it has no sub out I'm using the triangle Berea bro two speakers I'm finding this amp is lacking in bass.  I got about a $250 budget I want to add a subwoofer but I don't have a sub out how do I go about hooking one up to my amplifier any help would be appreciated 
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No i have no choice but to put speakers on desktop on small stands, i just have no room.  My setup is in a bedroom, so very very limited ways to setup, desktop seems to be best.  If i pulled the speakers out off the wall and into the room it would open things up im sure, just dont have the space.
Those dayton audio look good, has very good reviews on parts Express also great video on how to hook it all up and tune it in excellent thank you.