Actually, sprinters have exceptional quad development! Long distance endurance athletes.....not so much.
The biggest piece of advice I could offer you Jaysmiley is to get use to high rep leg training. I know there are many proponents of high rep training on this board, so this probably isn't the first time you're reading it. Everyone is different, but I think the legs respond best to higher reps simply due to the distribution of muscle fibers there (gotta be either type I - slow twitch or type IIa - use both aerobic and anaerobic metabolism to create energy, thus making them a blend of slow and fast twitch).
Never the less, get rid of your sets of 6, 8, or 10 reps. Keep your reps no lower then 12, ideally, 15-20 as far as I'm concerned. You pack as much weight on that bar or leg press or hack squat that you can handle, and you get down to business pushing out those reps. Implement progressive overload and strive to make progress week in and week out. Over time, your legs will become large for you, which ultimately will determined by your genetic make up, but never the less, they'll be larger and more sculpted than they are now.