Recommend a subwoofer?

If it were me, I would focus on getting a better preamp, given the speakers you list. They're pretty revealing and will most likely show the flaws in all the upstream components. If there is a budget issue, maybe get an integrated amp. The subs can come later, but if you don't get the main speakers sounding right first, you'll probably lose interest in building the system.

Thanks Zd

Well, the point here is to try to build something off of the old Nak pieces. Maybe those speakers are too revealing... I'm not a serious audiophile, though I am interested in investing in good equipment and really appreciating the music and movies I consume. Money is a consideration and there are annoying size constraints. The compact Class D Audio amp fits perfectly into the limited space I have for equipment. Not the most favorable conditions to build a system, I'm sure, but would be curious to hear where you would go with this if the Nak pieces and the amp were in place. Thanks...

SVS subs are well regarded and relatively inexpensive. Best of luck.

Ditto with SVS! I had the SB-1000 with a pair of Spendor
monitors and they were very good. They also have free shipping
and a 45 day in home trial. They are a great company to deal
with! You hook up a sub both L and R.

my personal preference is svs also