For In Search of Truth I'd go with The Masterplan, Misled,
and Different Worlds, maybe even Mark of the Triangle (It's a good
song, but I kinda got the idea that you needed to save space).
For Recreation Day, I'd say The Great Deciever and Recreation Day,
though I haven't listened to this album a lot.
Now for the good part; Symphony X.
Since I only have Divine Wings and The Odessey, I can only
recommend songs from these albums, but I'm fairly sure the
songs they offer will be impressive enough.
The Accolade (A must, definately the best song ever recorded)
Out of the Ashes
Candlelight Fantasia
The Eyes of Medusa (Really cool song)
Accolade II (See above. This one certainly competes with The Accolade)
King of Terrors
Well, as you can see, I'm more into harmonic, soul-soothing stuff
than power-riffs (even though I like those too), but I'm convinced
that these songs will turn your friend over if he's hard to convince.
Feel free to ignore me completely though. What do I know, I'm
just the new guy, right? Hehe.