The M1R has 4 Mb ROM, 16 note polyphony, and is 8 part multi-timbral with dynamic voice allocation. Each program (or voice) can use 1 or 2 oscillators and each oscillator has digital low-pass filter and filter envelope that is controlled by FLO's. Lots of options for modulation. There are 2 built-in effects processors with over a dozen algorithms. There are 100 programs in storage and up to 8 programs can be combined into a Combi (combination) which can be played together or split across your keyboard. The Plus-1 is an upgrade from the InVision Interactive giving you an additional 4 MB of multi-sound waveform data. It is in great condition, sounds great, and everything seems to be working as it should. No manual or rack ears.