Grado RS1e vs RS1i vs original RS1 headphones ?

Which one sounds better if any different?
I am well familiar with the newest RS1e but never heard the previous ones.
And another question. Would you recommend Grado headphone amp or something else to go along? For under $500, please, can be used in excellent condition.
This would be for nighttime listening Nakamichi 682ZX deck at moderate level. The Nak does have the amp and output level control. The amp is not too bad, listenable, but not good enough. Still, at this point I am more interested in phones.