Somebody certainly will correct me if I am wrong, I hope. But I do not believe an active external xover is mandatory to bi-amp these 2.5s. Just remove the bars on each polarity and throw the switch on the speakers themselves to bi-amp.
No, don't do that. That Bi-Amp switch enables different crossover components on the back of the speakers, which result in a wide overlap in frequency response between the EMIMs and the woofers. The point of doing this is so an external active crossover can select the 'actual' crossover frequency.
If you select the Bi-Amp position without using an external active crossover, you will be playing the EMIMs at quite low frequencies. In fact, this is how a great many of them got fried over the years on RS 2.5s.
The only [safe] way to Bi-Amp then without an active crossover is to do what's called a "passive bi-amp". This still involves a full-range signal going to each of your amplifiers driving the system, and the passive crossovers on the speakers would be set to the single-amp position. You will not achieve the benefit of a full active bi-amp this way, but
may experience some gains in clarity and dynamics.
The manual for these speakers is available on infinity-classics.de. You won't find another unit that does what the original crossover/equalizer does in exact function. But, there are many active crossovers currently out there which would allow you to successfully bi-amp the system (i.e., facilitate the crossover between the EMIMs and the woofer so that one amplifier channel drivers the woofer and another amplifier channel drives the EMIMs + EMITs). Rane, dbx, Ashley, Bryston...lots of them out there. All you need for this application is a two-way unit, although 3- and 4- way would also work fine as long as they are set up correctly. The closest thing you may find to the original in function (i.e., employing crossover and equalization) is probably to be found in digital units, like a Behringer 2496 or the DEQX units. I don't know a whole lot about their exact capabilities (I use analog crossovers on my system, so haven't read a lot about the digital units), but it's certainly worth investigating.
G~