This is what I was trying to say though about the cd player. If you plug ANY amplifier into a crappy source... it doesn't magically make the signal better. That's never going to happen. If you are even considering the th-900, you should seriously consider a dac. Anything you have ever heard about the signature dj, the th900, or any headphone: these people are using DACs and amplifiers, probably good ones. The TH-900 would not have this type of rave reviews if it was being listened to through magni/modi. Sorry those are not going to cut it for headphones like this. I haven't heard the magni/modi, but I can tell you I owned the more expensive asgard and I would not recommend it to any person for use with any headphone, and I especially would not recommend it to a TH-900 owner.
I'm not trying to sound rude here but seriously, go do some research about digital audio if you want to make an informed purchase. Like if you want to buy these headphones then go ahead I will not stop you it doesn't really matter, but if you want to make an informed purchase, just realize for either headphone to sound even close to its best, you will at the very least need a decent dac that will likely cost 400-500 dollars. And a reasonable amp. Something like the fiio E17($139) / WA7 ($999) / ALO Audio Pan Am ($500) / DacMini ($800) would not be a bad place to start since these are combo amp/dacs.
Mmmm... I don't think you need to spend that much money on dac/amps to get good performance. you can get great amp/dac combos less than $300ish like the new M-Stage Matrix or the O2/ODAC. Audio-gd and emotiva also has a really great value for price options.
the point is i don't think that spending more money equals getting better sound. you hit an intense point of diminishing returns. for example, you can easily get the stoner acoustic (DIY-company) UD110v2 DAC with the PCM5102A chip for $59 which is the same chip as the $1000 WA7 Firefly. I am obviously not saying that the sound quality is the same or anything, but there are many affordable options out there with great sound without breaking the bank