Used to have a monopoly.
For this i would mostly get a decent 4 note polyphonic Midi/CV. Vermona qMI 2 is great and super accurate (tested the built-in my perfourmer MKII) but a second hand Yarns or similar could do the 4 note chord job (yarns also have arpeggiator and portamento like monopoly, not mandatory since you can work it in the daw, but a plus).
I´d also get a few Hosa GMM-105 (or other stacking/mixing devices) to send the different trigg/VCO/ETC outputs to single inputs (VCA/ADSR/VCF,etc). Then similar routing with modulations sources and you´ll be pretty close in terms of functionality.
I was never in love with the monopoly filter.. i think that ajh will be more moogy and punchy, still get the doepfer or similar if you´re in for the closest sound possible.
As a plus, you can take a look to doepfer new polyphonic line and other QUAD modules if you want to save space, got more control on each voice, etc. The A-111-4 + quad VCA+quad adsr,etc, would save plenty of space there to fill with other modules (clock dividers/multipliers, modulator, etc), maybe you end up with something not so monopolish but with more interesting options...
