1. Well that solidifies my guess that it's not on 6DOIT, because everything but TGD has not been played since MM joined, except for scattered parts of 6DOIT (but not the song as a whole).
I guess if I go album to album (using data from setlist.fm)
If it's on Octavarium, it's either PA or TW, because nothing else has been played with MM exceot for TROAE, but they opened with that before. Each could be described as a "monster" track due to either heaviness or length, and the former is really a crowd pleaser, but TW doesn't really fit in this category. PA is not really all that remarkable as an opener, and they may have even opened with it before.
Could be Forsaken, CM, or TDEN from SC. ITPOE hasn't been played by MM. The rest are not crowd pleasers. TDEN is the most likely to be considered a "monster" track of the three due to heaviness and lyrics. I don't know if the other two have ever opened a set before.
On TOT, Endless Sacrifice does sort of check all the boxes, it's been played a lot, it's long enough to be monstrous by length, and at least to my knowledge, has not been used as an opener. I think it's the next best guess from TDEN. As I Am has also been played a lot, but it's been used as an opener. Everything else from this album pre-dates the Mangini days.
They've played everything from Awake too much for me to look up which ones they've opened with before, but I don't think they've ever done so with Scarred, which is on my "good guess" list. Also, other than tracks 3-5, they've played this whole album in the Mangini era, so it's hard to guess which other one it might be from this album. TSM and SDV are not monster in any way, and LSOAD isn't really either, so you can knock those off, too. 6:00 not unusual for an opener. I previously said it could be CIAW due to Epica having an identically-named song. So it could be tracks 2, 7, 8, and 10 off this album.
ADTOE is just too hard to narrow down, because it's all been played during the Mangini days. BITS has been used as an opener, and OTBOA is not remarkable as an opener in any way. But there's two good crowd-pleaser choices from this album in BAI and Outcry. And Outcry hasn't been played all that recently (2011 was the last time).
SFAM is probably the hardest to guess, since a lot of it has been played since MM has joined the band, and there's too many songs for me to check if they are the opener.
For FII, ToT fits the bill. So does Peruvian Skies, but that strikes me as a good opener, and they might have even opened with it before (they've played it too many times for me to look it up. But it also has the "monster" lyric, and we know there's a FII track in the set somewhere.
Best guesses given the above, in order of what I think, are TDEN, Endless Sacrifice, Breaking All Illusions, Scarred, CIAW, Trial of Tears, or something from SFAM that they haven't opened with yet.
Of all of these, the only one I see any significant relationship with to Epica is CIAW due to song name. It doesn't strike me as an unusual opener, though.
I guess it doesn't have to do with an individual song name or lyrics. I think I'd probably take CIAW off then.
IOW, I'm still confused.