I purchased a 2nd cassette deck from Ebay for my 2nd system. It too has the dbx noise reduction facility so I'm really interested in seeing if tapes recorded on the Yamaha with dbx will play cleanly on this deck.
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No reason why they shouldn't, DBX encoding / decoding is proprietary, so it won't matter whether the original deck and the playback deck come from the same manufacturer. They license the technology from DBX; there's no option to modify it.
DBX encode/decode is very capable, S/N ratios into the 90dB range is entirely possible, even with cassette.
The one thing that hinders the adoption of DBX encoded cassettes is the limited number of car decks that can decode them. For that reason I prefer Dolby C which is near-DBX as far as noise suppression goes but is a bit more common in aftermarket decks (lower licensing and hardware costs).
However DBX does have one advantage in that you can buy decoders or encode/decode units that will add DBX capability and work with any deck. I don't know of any external Dolby C decoders. Bonus: there actually are DBX-encoded vinyl LPs, which would be usable with an external decoder.