Dice probability spreadsheet

I'm a board game hobbyist in need of an Excel calculator for probabilities of adding ANY combination of results from rolling a mixed pool of dice of various sides (d4, d6, d12,...). For example, what is the probability of a "5" by with ANY combination of two 6-sided dice and one 8-sided die? If any of a roll results are a 2, 5, 7, that is a "hit" because of the middle die result of 5. If I roll a 2, 3, 6 that is also a "hit" because 2+3=5 (and I just toss out the 6). I want to input the number of sides to a pool of dice, input the values that I need probabilities for, and input the total amount of incremental modifications to the dice results (both increases and decreases). This is a mathematics-bases job for a project that doesn't really have a budget. I'm just playing with numbers for now. Maybe sometime in the future I'll legitimately make a game but I'm just experimenting now. I'll likely release the resulting excel document online for free to other board game designers.