While a lot of their songs wouldn't be able to work with Rock Band, after listening carefully to each song for each instrument part I found a few that should be able to. The songs are heavily based upon the singer and though the guitars and drums come in a few seconds later then the singer, this wait is nothing for the singer on some other songs such as GGHT and Foreplay.
I will list the songs, points I noticed and timing when the other instruments came in, a link to the youtube video of the song, and suggestions on how to make the songs work for the game. Special note, these are not my youtube videos, some nuts mixed the song with anime images, just listen to the music and the rhythms.
Singer starts immediately while the drums and guitar parts come in at 37 seconds. While the entire song has a piano going through it, this could be switched to the bass part, since I know Still Alive didn't really have a bass part either and you improvised. The singer echo part and chorus line at 2:30 could just be the main singer voice which is easily distinguished from the rest of the chorus.
Obviously this song is almost purely based around the singer, with the other instruments backing him up. While I think the guitar part wouldn't be overly difficult, the singer and drum part sound fairly challenging which would make this a more expert style song.
The piano part plays for the first 17 seconds and then the singer begins singing. At 54 seconds the guitar and drums come in. The drums mostly have cymbals at this point while the guitar is playing various chords. They then play again at around 1:30. A Guitar solo starts at 2:50 with a mellow drum beat accompanying it. The guitar solo sounds very difficult in a few parts and fast paced. at 3:57 the solo ends with just a piano playing and at 4:22 the song ends.
I feel that once again the bass should be playing the piano part, and the song might be able to be edited slightly to better suit the bass sound with the piano. The singer doesn't sing for 2 minutes of the song which is still reasonable when compared with other songs. At the very worst, the last 30 seconds of the song could be cut off where it only has the piano playing and the song could go to the ending of the solo.
What Is Eternal
The piano plays for the first 20 seconds and then the singer begins singing. The drums plays softly starting at around 25 seconds. The guitar comes in at 52 seconds. There are a few breaks throughout the song between guitar parts, but they are only around 5-10 seconds a piece. The Ode to joy on the piano starts at 2:52 and continues to 3:10. This could be used for a small break, such as the long wait on Foreplay or Won't Get Fooled Again. The rest of the parts after the Ode to Joy piano break continue until the song ends at 4:39.
The instrument parts are at a decent challenging level, the singing part sounds extremely difficult (and fun) and the song is pretty well balanced between all the parts. The drums are mostly playing cymbals softly at the beginning and then become one of the main parts in the chorus areas along with the guitar where they blend in with each other for the rest of the song after 52 seconds till the end. The bass could once again take the piano part.
I feel these would be good selections because while they are fun for all instruments, they are a lot of fun for the singer. I've been feeling that most of the dlc lately has been pointed at instruments rather then vox, and I would buy these dlc in a heartbeat. I feel that many other people would share the same interests (or at least I hope so) the song is fast moving, powerful lyrics, and challenging rhythms. I hope that you can give these suggestions serious considerations because I spent a lot of time listening and writing this out.
To players posting, please read this and listen to the songs before just seeing the title and saying you hate TSO or it won't work.