Wow - do you have a weak line-out on your source, or how loud do you listen? Most portable amps I've tried have no problems driving the T1 to adequate volume. To drive them adequately to their potential (especially the bass) is of course a different story. I'm at work now - will advise SPL levels when I get home and have a chance to test on a few lower end options.
No I don't have a weak line-out and I don't think I listen to ear-bleedingly loud levels either, but the portables I tried - to name a few, Pro-Ject Head Box, RL Concero HP, Lehmann Linear, FiiO E17 - were all lacking in the volume department, especially with quieter recordings. Maybe I just haven't tried the right ones!