The key to epic orchetral music is to have driving percussion (and lots of it), along with a very pronounced melody. Whenever I write something I want to sound big and epic, I almost always double the melody in octaves throughout the orchestra. Violins may have the melody, and violas may double the melody an octave lower. Or maybe horns will double the melody an octave or two down. A counter melody is nice, but only add one after you're sure the main melody is in the forefront. As a side note, strings make very good percussive instruments. They can be used to help the percussion drive a piece forward.
The second thing you want to be aware of is the chord progressions. Keep them simple, and try (as much as possible) to keep everything in root position. This means that the double basses will always be playing the root of each chord. This will keep the progression feeling rock solid and powerful. Once you start putting in inversions of chords the foundation of the piece will begin to become weakened, as inversions tend to be less stable sounding than root position chords.
For some music to check out, you could have al listen to Metal Gear Solid music, (pay attention to the last couple of minutes). Also, if you're using Hans Zimmer as a model, I'd go back and take a look at Gladiator, Lion King, and Rain Main. Although the later two aren't the most epic of sound tracks, they do have some pretty powerful moments in them. Some of the World of Warcraft music would also be worth a listen. This piece is a good example of the strings driving the music. Without the strings, the music would be bland and would drag on.
I'll probably jump back here if I can think of anything else, but I consider those points to be the most important. There are plenty of better music examples than my works here on Newgrounds, but I'm honored you're using my music as a model!
