My upscaling method - which took some time in tinkering, tweaking and optimising, has now become much more powerful than simple staightforward 'upscaling' per se as it involves the usage of a few VST plugins, one of which is Halo Upmix by Nugen.
The tools I used are not freely availabe but the end resault to my ear sounds far superior to anything I tried before. It enables total control over systemwide audio at the cost of relatively low and acceptable latency (~11ms) using standard Windows DirectSound (KS) as backend as opposed to something like ASIO or even WASAPI.
Audio interface: NVIDIA HDMI Audio
Audio 'capture' and output software device: Virtual Audio Cable
VST host: Blue Cat's PatchWork
Audio Upscale: Nugen Halo Upmix VST
EQ and MultiBand/MultiChannel dynamic processing: FabFilter Pro-Q 3 VST
Limiters (one on input chain, one at end of output chain for general gear protection): ToneBoosters Barricade VST
Subtle low end saturation enhancement: FabFilter Saturn VST.