Increase volume of rented iTunes movies?

Question

I have difficulty with the volume level being too low on rented iTunes movies.  I have tried the following setups with my first generation iPad:
1) Apple HDMI adapter -> HDMI cable to Mitsubishi EW230U-ST projector; Creative T-40 speakers plugged into mini-stereo jack of projector; volume turned to max on all devices.  This produces speaker volume that is not adequate for a large room.
2) Same as #1, but instead run the Creative speakers directly from the headphone jack of the iPad.  Volume similarly inadequate.
3) Same as #1 or #2, but insert FiiO E5 Headphone Amplifier into mini-stereo chain going to Creative T-40 speakers.  This produces adequate volume, though to my ears, the quality is diminished somewhat.  I'm not fond on this approach, because the FiiO uses a built-in battery which might fail without warning during the showing of a movie.
What would be ideal would be a way to increase the volume going out the headphone jack of the iPad.  I understand that this is deliberately limited to protect the hearing of those using headphones.  Alternatively, increasing the volume going over HDMI would likely help - unless the projector's mini-stereo jack is similarly being limited for headphone reasons (less likely, since projectors are usually hooked to external speakers).
So ... is there any way to make the iPad output louder sound with rented movies?  Jail-breaking solutions are probably not appropriate, as I don't want to risk my ATT unlimited data plan.
I should say that if I just play a DVD instead of using the iPad, the sound level from the DVD player's stereo jack is strong enough for the Creative T-40 speakers to rock the room.
If I could solve this problem, I would rent a lot more iTunes movies, as it is the easiest way to get a movie.

Answer 1

I followed your procedure and did some testing.  By setting the volume slider to +100%, the movie was louder on my Mac.
I then transferred the movie to my iPad and took my equipment to the facility where I play movies. I didn't have a pristine rental copy to test against, so I used my own DVD copy of the movie.  This is what I found:
A) The best and strongest sound was when the the T40 speakers were directly connected to the DVD player's RCA sound jacks and the video was coming thru the hdmi to the projector.
B) The worst (quietest) sound was when the speakers took their input from the mini-stereo jack of the projector, with the video and sound coming from the dvd player thru hdmi.
C) I compared this with the +100% sound-increased movie rental running on my iPad, with hdmi connection to the projector and sound coming from the mini-stereo jack of the projector to the T40 speakers.  This was definitely much louder than "B" above.  So I can safely say that the sound boost performed on the rental movie on my Mac did copy over to the iPad.
D) Unfortunately, even "C" above is not loud enough for this room.  But if I added the FiiO amp to "C", then there was plenty of sound - though not as pleasant (or simple) as "A" above.
I wonder if there is some way to get more than the +100% sound boost in iTunes?
I think it is unfortunate that renting a digital movie is fraught with such difficulty. It should be possible to adjust the sound as needed - and preferably on the iPad!  Otherwise, we are just going to keep renting DVDs.