I’m having difficulty finding playback devices for old 8 track &cassette tapes. Does the quality of the playback device effect the quality of the audacity conversion?
Certainly does 
the old IT adage GIGO applies (Garbage In - Garbage Out) …
These two articles from the Wiki may help:
http://wiki.audacityteam.org/wiki/Recording_from_Cassette
http://wiki.audacityteam.org/wiki/Cassette_Deck_Magnetization
WC