Some initial thoughts...
The board
It seems a little odd that the board array is being passed into the TicTacToe class. I think if you really want to inject it as a dependency into the TicTacToe class, then you'd be better off wrapping it in a class. Alternately, the simpler option would be to make the board a private member variable of your class, which it then has complete control over. As it stands, both your main and your TicTacToe class have intimate knowledge about the array and it's size, although the class doesn't validate this in anyway, so if the caller creates an array that's too small things will start going wrong.
Checking for tie
When you're checking for a tie, you're checking for upper and lower case players ('X' and 'x'). If it wasn't for the fact that the array is being supplied you'd be guaranteed that 'x' wouldn't occur, since you only insert 'X's into the grid. You do the same 'X' or 'x' check when allowing the player to make a move.
Winning condition
When you're checking for a win, you're trusting the caller to pass in the correct player ('X' or 'O'). If the last player to take a move was 'X' and they placed a winning move, but checkForWin was called with player 'O', it would declare 'O' the winner, even though there is actually a line of 'X'.
Checking for line wins (horizontal + vertical) is easily modelled with loops, which will help to simplify your checkForWin method. I'd also suggest taking the winning player from the board, rather than from the supplied parameter.
Prompting
You convert 'X' to 1 before prompting the player to make a move. Why not just have it be X's move?
std::cout << "Player " << playerTurn << " please make a move" << std::endl;
Variable Naming
In your playerMove method, you're using 'x' as an iterator variable:
for(int x = 0; x < 9; x++)
Given that 'x' actually has some meaning in your game, I'd consider using a different name, even if it was just 'i'.