Hi,
I currently using a 9000ES and it's very nice. I've previously used a TA-E1000es (prologic only) in combination with an EP-9es (90es has mpeg audio as well as DD) to give me Dolby Digital. The 9es is essentially a digital preamp with onboard DD and a 5.1 passthru.
I use the 9es to give me some extra digital inputs to the 9000. I can select any of the 4 digital inputs to the 9es and feed an optical output to an optical input on the 9000. I then select the 'bypass' on the ep-9 so I can hear the (analog) output from the 9000. Sometimes, I just use the output from the ep-9 although the version 2.5 firmware on the 9000 has a virtual 6.1 mode which is quite useful as I don't really have the room to install a 6.1 or 7.1 system.
The overall sound quality from the ep-9 is very good and it had very good reviews in the press. It was rated pretty well by Stereophile Guide to Home Cinema as well and was a 'recommended' component. I've seen the Ep-9es and 90es go on ebay for around £80 which is a bit of a bargain. Some people have reported problems with 'noise' on the volume control but I've never had any issues with it.
Brian