I am wondering how deep is the bass on these Tennoy's?"
I do not think Tannoy inc' would be upset if I said the 5As do not go that low or that loud but that is not why I bought them. I have a very small room and the monitors were primarily bought for mixing at modest levels but they do have a suprising amount of "heft" for a 140mm driver, clean and un "hyped" as well. My son finds them fine for his main interest which is jazz.
I would think the larger 200mm speakers would be ok but to reproduce the full frequency and dynamic range of a concert grand is beyond all but a few (expensive!) speakers.
I think most of the experts here would agree that unless you can afford a really good integrated speaker/sub system do not go there and in any case the not insignificant amount of money would still be better spent on a better two cabinet setup.