Hi MV. First, we're testing the DVD-2500BT with a variety of appropriate amps, but most often with the Denon AVC-A1HD (£3800). Video is being fed into our reference Pioneer PDP-LX5090 plasma, although we've also tried JVC's DLA-HD100 projector.
Now to the optimum settings for your Onkyo's video scaler. With a 1080p video input from Blu-ray, the TX-SR875's onboard video scaling and processing is bypassed, no matter what scaling mode you've set it to. This is why your Pioneer plasma is still showing a 1080p input even if you've set the Onkyo's processing to 720p: the native 1080p content on the Blu-ray disc is simply passing through the Onkyo directly into the Pioneer. And yes, I know you've not set the Onkyo to 'through' mode, but still - this is how it treats 1080p from Blu-ray (I checked with Onkyo just to be sure, too!). There's no reason to feel downcast about this, by the way. All it means is the picture you're so enjoying from Blu-ray is being provided by your Blu-ray player, with no additional modification save for the work the Pioneer plasma panel is carrying out.
And on that subject: when you're viewing DVDs, you're currently carrying out two video scaling processes. First, you're taking the native 720 x 576 content on the disc and scaling it to 1280 x 720 (inside your Onkyo). Then, you're scaling your video again to match the native resolution of your plasma panel (1024 x 768). Now it could be that this is, in fact, the best way to go: the HQV processing in the Onkyo is very good, as we've said many a time.
But I think you should also try omitting the Onkyo's video processing from the signal path too, just in case. You might (note I said 'might') find that only using one scaling process (ie 720 x 576 from the Blu-ray player up to 1024 x 768 in the Pioneer) delivers better results. Pioneer plasmas have decent scalers - it's one of the many reasons why they're so good. Give it a go, I'd be interested to hear how you get on.
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