Update on the Motorola DSP 56300 emulator, for the Access Virus C plugin (called Osirus):
The generous developers community’s website provides the software instrument also as a Linux Arm64 (aarch64) package, either in VST2, VST3 or CLAP format.
To my limited understanding, using Osirus in Zynthian should just require a VST Linux wrapper, and as soon as ZynthianOS switches to aarch64 it might be possible to exploit the RPi5 improved CPU performance, to sustain the required DSP 56300 duty-cycle (136 MIPs for the Virus C implementation - for a comparison, the test console provided by the developers returned 460 MIPs on my i7 quad-core iMac).
As for the Access proprietary synthesis program, I quickly traced a third-party open repository with both the Virus B and C ROM (reverse-engineered?) software, that the 56300 emulator site cannot provide for obvious copyright infringement reasons:
Today I have had a try at Osirus on Cubase/Mac, and - my goodness - it simply sounded phenomenal, going straight away in the top region of my preferred software instruments, be them freeware/open source or commercial.
I think that embedding Osirus in a future stable release of ZynthianOS would greatly improve the synthesisers armoury of this project, complementing the features of the local Swiss army knife Zynaddsubfx quite perfectly.