I'm not sure what a T-bar is, is that a bar that attaches to a cable machine?
I bend over as close as possible to a flat angle when I'm doing the bent-over rows. Pick up the bar deadlift style and my knees are slightly bent, my back is at about a 20 degree angle to the ground ideally, maybe more like 30 if I'm doing heavy weight.
I don't think your lower back should be sore the next day, and it definitely shouldn't hurt in the process. Use good form and be sure to SQUEEZE the upper back as you lift and lower the weight. The only way I can imagine the lower back being sore is if you were rowing some SERIOUS weight and picked it up deadlift style.