I seem to remember the 99pre was criticised for being a mediocre product when compared to the 909. I've just resurrected mine after five years and have made up a balanced cable to run from the D type ampbus output to my power amp's xlr inputs (a fiddly job).
I've recently been using a Benchmark DAC as a pre and before that a TVC passive (which was a disaster with my power amps). Somewhat surprisingly, the 99 sounds remarkably good. The difference is not at all subtle. It does have excellent features and the ability to alter input sensitivity is useful.
I wonder how much better a far more expensive preamp would sound (probably not much). It seems that component matching is far more important than cost per se.