While it has an upfront cost, I’d say the best way to play old consoles is by using flashcarts/ODEs/softmods and a proper scaler like the Retrotink 5x Pro or the Open Source Scan Converter. Those scalers take a multitude of inputs, scale and digitize them for output over HDMI. The RT5X can even do crazy stuff with filters to emulate CRTs and other effects.

That said, doing all of that comes at a cost. SCART cables for each console are about $40 each and the scalers run ~$325 for the RT5x or $120 for the OSSC. Then if you want to get a way to switch inputs, thats another $50-200 there too. Worth it if you like your old consoles, but to just revisit that’d be an expensive proposition. Is a great way to futureproof them, even moreso with the upcoming Retrotink 4k but that thing won’t be cheap. (Estimated price is ~$1000)

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If you want to do it on the “cheap” but get as close to the originals, I’d highly suggest getting /making a MiSTer setup. This uses a FPGA to do emulation via hardware, which is about as close as you can to the originals providing the code is up to par. That’ll run about $300 all said and done, but gets you a crapton of systems all outputting over HDMI.