If I use a Benchmark DAC-1

In my experience, there is no difference in the sound quality with various transports. Other listeners over at Audio Asylum have reported differences between transports, so my findings are not universally held. If the opportunity to test (beg or borrow) a variety of transports, listen for yourself and you'll have your answer. I would keep your current transport and save the money for something else.

For the money you can't do better than the Benchmark. I had one while my many times more expensive Bremen No.1 dac was in Switzerland for repairs and was amazed with the sound from this piece. My pro audio brother who laughs at audiophilia recomended it to me when it first came out. The beauty of this DAC is that it re-clocks the very poor signal from your carousel and sends pure jitter free sound to your preamp. You will be amazed with the resolution and clarity from this bargain priced piece. Oh yes, it will blow away the Sony. Unless you want to spend many thousands more, buy it and be thrilled!