I have Triangle Titus also. Wonderful speakers that do what they do very well, but low bass extension is not what they do, so generally a very good candidate to supplement via sub(s).
If you do not care about or need bass extension below 50hz or so to be happy, I'd go sans sub with the Titus and get them to shine as is.
If more full range sound is the goal, I'd focus first what is needed to get sub integrated a best as possible for best sound without "muddying the waters".
From there, I would think about using two matching subs in order to help normalize bass response throughout the room further is bass is good in one listening position but not so much in others. Next step beyond that for same reasons would be to add additional subs, but benefits become increasingly marginal from there.
If you do not care about or need bass extension below 50hz or so to be happy, I'd go sans sub with the Titus and get them to shine as is.
If more full range sound is the goal, I'd focus first what is needed to get sub integrated a best as possible for best sound without "muddying the waters".
From there, I would think about using two matching subs in order to help normalize bass response throughout the room further is bass is good in one listening position but not so much in others. Next step beyond that for same reasons would be to add additional subs, but benefits become increasingly marginal from there.