A cheaper Proteus 1000 model was also introduced with the same soundest and ROM but only 64 voice polyphony and fewer individual sound outputs. It could be expanded with slots for three additional sound ROM cards. It featured up to 128 voice polyphony and 32-part multi-timbrality. It contained many 'bread and butter' sounds, among just over a thousand waves utilising 32 megabytes of ROM. The Proteus 2000 released in 1999 was a 1U rack sound module based on Audity 2000 released in 1998. However, they could be also upgraded by obtaining XR versions, having extra read-only memory (ROM) for more sound patches, that would have 384 each.

The original Proteus trilogy contains 192 patches each (Proteus 1, Proteus 2 and Proteus 3).

The available ROM chips included the Composer, a work-horse set of sounds useful for popular music production, three orchestral ROMs, the Vintage Keys collection of electric organs, pianos and classic synthesisers, a chip dedicated to the Hammond organ and a drum ROM as well as the Orbit and Mo-Phatt collections, aimed at dance and urban genres and the Xtreme Lead, optimised for monophonic synthesiser soloing. However, since most allowed four ROM chips to be mounted, and these chips were available separately, real differences might be simply cosmetic. The Proteus range was developed into several models, some differing from each other only by the sound banks they contained, which were optimised for different purposes. The exclusive license for re-formatting and managing historical E-MU Proteus sound content has been acquired by Digital Sound Factory. This type of sound production dominated electronic music production for several years in the late 20th century. However, unlike a true sampler, such devices do not allow the user to record sounds but instead offer a range of factory sounds suitable for any given use. These sounds may then be layered, filtered, modulated by low frequency oscillation and shaped by envelopes. Unlike the true synthesiser, sample-based equipment does not derive its raw sounds from electronic oscillators but from recorded sounds held in read-only memory (ROM) chips. E-mu Systems came to prominence in the early 1980s with their relatively affordable Emulator sampler, and subsequently pioneered sample-based synthesis technology with the Proteus range.