I am a HUGE fan of the 1704s and have owned numerous pieces, too many to count, with them. The 63s are something special.
Had them both over many dacs and cdp's, and tinkered and modded them to the hilt.
The PCM1704 is top dog for all Redbook pcm, far lower noise, almost glitch free, so it doesn't upset wide bandwidth I/V stages as much.
Cheers George