have you tried using DSP studio ?... which is, arguably, one of the best DSP engines available at any price. If that is not sufficient, add a VST pluggin.
You are losing out on a bunch of things, strictly my humble opinion here, but using freeware that forces you to upsample or downsample and not use exclusive access ... seems to defeat the purpose of the fine audio playback engine that JRiver includes. Maybe you are just trying to shorten the learning curve? What are you looking for that this software has that JRiver doesn't already include? then you could use wasapi exclusive or ASIO and get bit-perfect playback without going through windows or flip to make it sound like you have the echo of an arena if you want. Might be surprised at some of the options already incorporated, without any need for pluggins or external software.
