Not a 100% sure what you are asking, but as I understand it you want to find the 2θ angle of your peak in a diffractogram?
If so the calculation should be straight forward. I.e. use whatever miller indice you want, find the corresponding d- value (i.e. plane spacing) for your specific lattice...
Hi I guess you could use PowderCell to visualize the structure. You can define your own structure from atom coordinates and symmetry of the unit cell. There are some structures included in the install file, but I don't remember if it includes SiO2 or TiO2. The program also simulates powder...