Recommend a subwoofer?

Hello... Nice old Nakamichi pre-amp (610) and tuner (630) will likely be connected to SDS-440C Class D Audio Amplifier which will power a pair of Mark & Daniel Maximus-Mini+ speakers (open to thoughts on that since they are not purchased yet).

Can anyone recommend a decent subwoofer to complement this set up? The room is about 20 x 15 x 9' with an extra nook on one side.

Also, pardon my ignorance, but since it's a two channel amp, how to best connect the sub (left or right)?

Many thanks...
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...
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.
If price is a consideration, check Parts Express Dayton Audio line of subs. You should be able to find a few under $200.
I have had good luck with a pair of JL audio E112s. I can't see a need for anything "better". They have built in digital crossovers (high and low pass) and are designed to be connected between the pre-amp and power amp and high pass to the mains above the crossover set point.
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As another possible choice is the Rythmik Servo subs. They are also very well received in 2 channel systems. And they too connect via the L/R to your PA.
Another vote for Rythmiks here. I replaced one Rel with two Rythmiks - for the same money - and couldn't be happier. Very, very good choice.
I own Rythmiks and can recommend them without hesitation. Great product.

The SVS subs have an excellent reputation and their offer on a pair of SB 1000 would appear to represent a great value.