Rich,
The big jump in electronics difference comes when you add a second low-pass filter on the bass like the signature electronics package. Europa / Rogue has only one filter with a pickup pan control. You can get quite a lot of sound variation by setting the filter to resonate where you like the tone center, then altering the pan to change the color or emphasis. With 2 filters, you do something similar, but you have a filter for each pickup, so you have more tonal control. You can dial in a really peaky tonality on the bridge pu, and then dial in a mellow bassey sound on the neck pu for a complex character. Or.. the opposite. Or.. both pu's really peaked out (high Q switch setting), or.. the opposite.. really bassey on both for a killer Dub sound. Series electronics has a pu selector switch which allows quick tone changes, stereo sound, and more combinations. However, I am delighted with my Europa for simplicity and live sound with the bass and treble quick change boost switches. I would definately recommend the filter upgrade for your Epics. I did this for my Epic 5 string fretless, and it really helped make it a keeper. Go for the 3 position switch for more sonic flexibility. Also, I just upgraded my speakers from an SWR Goliath 4x10 & Big Ben 1x18 to an AccuGroove El Whappo, and the sound quality went from stage to studio. A great cabinet is sometimes the best investment in sound. You can't go wrong with the SF-2 either.
Kris