I've been in a different country to the opera for two weeks now. Vs. our homemade passive pre, the opera reduced the dynamic compression which can result from the use of a passive pre, and had noticeably more treble detail. For it's price as a secondary function of the product, I would guess (I haven't listened to many ss pres) it represents excellent value if bought to be used as well as the hp amp. It doesn't seem to add any strong or unpleasant colourations, but has enough warmth not to sound like some typically colder SS products I have heard.
The opera as a pre could be said to match it's sound signature as a hp amp pretty closely. As I use the opera with hd650s, which are far warmer than an average speaker/power amp combo, I prefer a tube pre in our system, but use the opera due to certain practical constraints. TT to tube phono stage to opera sounded good, although I only listened briefly.
From memory, saint.panda has written elsewhere that the opera, like other corda products, lacks depth in soundstage compared to some other hp amps which perform well in terms of soundstage depth. With the opera as a pre, the sound stage did not gain any depth vs. our passive pre, but may or may not have been limited by our system.
Our system is, Luxman tt (don't remeber the model) to ARC SP-12 phono or sony XB930QS as cdp or transport - to - opera dac/opera - to - perreaux PMF 3150- to - Celestion 7000s (old but good). The CDP dac is probably the weakest link, although with the passive, it's forward sound suits the system well. We now use the opera dac.