This will fix the "distant" effect he's hearing. The 2 together (the headphones and amp) will provide a recording studio like quality sound.
I do wish more reviews and ads for headphones pointed out the headphone amp requirement because it catches a lot of people off guard and they blame supposedly poor sound on the very high quality headphones because they weren't aware they needed to be paired up with an amplifier.
The pc350 are easily the better set of headphones. While the use a headphone amp may be an inconvenience, the sound quality of the set (and even the quality of the mic) is far better and worth the amp requirement.