Re: A few words about...™ Iron Man -- in Blu-ray
The lossless track probably (can vary of course) has greater overall dynamic range than the lossy one. I find this to be the case when I compare some of my SACDs with their CD counterparts. Because of this, I have to turn up the volume for my SACDs compared to the CDs for the "oomph" to be in play. I have noticed a similar phenomenon with "lossless" tracks on BD and HD DVD (though I only get the "core" of the stream, that "core", when compared to DD/DTS on SD DVD, appears to have a wider dynamic range--my impressions are anecdotal, of course, as I don't have full "lossless" capacity for HD DVD/BD but it tracks with my SACD/CD experience). The solution, for me, is quite simple. I turn up the volume. Of course, when level matched, the perceptible difference between lossy and lossless pretty much disappears (except in those cases where the differences in dynamic range are dramatically different--but even then, with a movie's visuals occupying a great deal of one's attention, noticing those exceptions requires an effort that transforms the event from something entertaining to something requiring "work").
When I listen to music (rather than watch movies), I tend to be more focused (no visuals to distract me) and I can, if I try, notice the difference in dynamic range between a CD and an SACD or DVD-A--but that difference is only valid if the mix and mastering is the same. Not all that common (and that is only applicable to 2 channel. In MCH, my preferred mode of listening, the MCH mix far outweighs whatever benefit I'm getting from "lossless".
Now, if I had an acoustic listening space that was ideal, the differences might be more dramatic--but while I've done a decent job at treating my room, practical and financial considerations prevent me from going "all out". I've already taken room treatments and eq'ing my sub and judicious speaker placement (and selection) and so on to a far greater degree than anyone I know (outside fora like this) would consider worthwile (or even sane

), so I've reached what I consider to be a diminishing margin of return. I'd rather spend my time enjoying the movie and music.
Sorry, I've veered a bit off topic.
Back to your receiver--are you using a BD player with MCH analogue outputs? If so, I would just set the levels in the player to compensate. If it is connected via coax/toslink digital, then you have the lossy core signal coming to your receiver (as I have with my setup) and turning up the volume is the easiest solution (that, or selecting the lossy track as you are currently doing).