Half the synths you mention you CANNOT emulate with the Origin today. Matrix-12, System-700, or good lord an Arp 2500, none of these models exist in the platform. These synths have very characteristic VCO and VCF responses that while you may be able to create a "patch" that emulates the routing to some degree, it certainly doesn't emulate the characteristic "sound" of these classic synths. Especially the Matrix-12 since there are no Oberheim models available for Origin, especially the Matrix/Xpander multi-mode VCF section.
Well, that is true in a sense, as I was coming down with something last night I should have said "something like these synths." You can't emulate the poor shielding of the ARP 2500 matrix system, allowing control voltages and audio to bleed all over the place. However, the 2600 has a definite ARP character handed down from its massive father, and the Origin allows you to make a very authentic ARP modular in the sense of the 2500, which the 2600 could only hope to achieve with three or four of them wired together.
But as for the Matrix-12, I'm more sure of. The use of the Curtis family of audio ICs coming into widespread use at the time are quite similar to the sound of the Origin modules, and I've been able to get some very similar sounds to the Prophet 5 and OB-8. I haven't tried to get an actual Mx-12 patch yet, since that monster is very complex, but someday I'm going to put my mind to it, especially if Arturia blesses us with Oberheim modules. While it won't sound exactly the same, it's going to be close enough, until I can finally grab one of my own.
On that note, being something of an analog purist, I will say that if you have a real Mg, ARP or dare I say it, CS-80 around, the Origin and Arturia's softsynths come very close, but still lack a little something the originals deliver, as holografique says. But seeing as I can't afford the originals, and the quality of the Arturia modeling is very high, I don't quibble over small issues and happily program and play away. Besides, a real Mg Modular III in good shape can cost as much as a house!