Firewall is down on both PCs, ping and telnet initially worked OK in both directions, now after total rebuild they don't, but each PC can separately telnet to the default gateway, and Control-PC can't see Audio-PC via JPLAY. Correct?
I may be grasping at straws here, but is it possible that before the rebuild there may have been something amiss in the JPLAY registry settings that prevented the Control-PC seeing the Audio-PC? Then after the rebuild the ip address on the Audio-PC changed (I've seen this happen when installing new OS versions before)?
So have you checked the ip address (via ipconfig in a command prompt) on the Audio-PC after the rebuild? If not, it would be worth checking just to be certain.
Sorry if the following seems too obvious but I'm just trying to cover all bases so please bear with me (better to be safe than sorry). Can you confirm that in your registry settings you have:
Audio-PC = name<name of Audio-PC> ip<correct Audio-PC ip address>
Host = correct Audio-PC ip address
Single PC Only = 0
Streamer Destination = correct Audio-PC ip address
Control and Audio PCs
Dell Inspiron 15R SE laptops with Intel Core i7-3612QM (2.1 GHz) and 16 (Control-PC) or 8 (Audio-PC) Gb DDR3 1600 MHz RAM
Windows Server 2016 with Audiophile Optimizer 2.20 beta 5 in Virtual Core Mode on Control-PC (via Fidelizer 7.4 free, modified CAD Desktop Services Killer Script and manual software tweaks) and on Audio-PC (via Fidelizer 7.8 Pro and 7.4 free, CAD Windows 8.1 Optimization Script, modified CAD Desktop Services Killer Script and manual software tweaks); JPLAY 6.2 with ULTRAStream engine; JRiver MC19 as DLNA Server; Upplay 1.2.8 as Control Point; Process Lasso Server Edition 18.104.22.1682; Q-Dir 6.69
Control-PC > SUPRA Cat 8 Ethernet Cable > Audio-PC > Chord Silver Plus USB Cable > Uptone Audio Regen (Amber) > Curious Cable USB Regen Link > Luxman DA-06 > Chord Chameleon Plus XLR Interconnects > Luxman L-505u > Van Den Hul Teatrack Speaker Cables > Bryston Model T Signature Speakers with external crossovers
Samsung Story 2-Tb ext HDD (USB to Control PC) plus two 3-Tb Seagate backups