Two subs, yes or no?

Bob is correct. 2 is better than one. With 2 mono subs you will be able to minimize room effects, esp. if located asymmetrically in the room. There are also advocates of stereo subs for music, there is only a mono LFE track for HT. If you are going with a stereo pair, I would locate them near your mains, but still asymmetrically (one inside left main, one outside right main, for example).

If the pre-amp has variable line outs, there will be a left and a right. In that case, if you run one direct to each of a pair of subs, they would be a stereo pair. However, the pix of the rear apron of your mcd201 here (http://www.mcintoshlabs.com/images/products/MCD201Back.jpg) shows one set of variable RCA outs and one set of fixed. Without an active x-over of some kind, you would not be able to level match the subs to the mains unless the XLRs were active at the same time and either your sub or your amp accepted XLR inputs. Same answer as far as hook-up, tho. You would connect right output (xlr or rca) to right sub and left to left. Alternatively, you can take the full range signal from your main amp and either route it through a sub(s) (with a high pass filter) to your mains, or parallel the sub(s) with the mains by running speaker cables to the sub(s) and the mains from the taps on the amp. I admit, its confusing. If your main use is HT, and if the output (volume) of the LFE track is sufficent, then I would go with a single, higher quality sub. If your use is mainly music, I would go with 2 subs if your budget can take it. Stereo or mono, depending on the equipment you are using.

You will have to experiment for sure, but the idea of asymmetrical placment is to (theoretically) help with room modes. If both the balanced and RCA variable outs are active, that will help, but you may have to compensate for differential gain via se and balanced circuitry IF it is truly balanced and not just an XLR connector wired to se circuit. If not, then the differential gain issue disappears, and could be handled of course when adjusting sub gain to match mains.