Copied from my rely in another thread....
The RX-666 and RX-888 are similar. Both are based on the BBRF103 open-source design. The RX-888 adds an integrated LNA, plus claims of possibly a higher-precision TXCO, for around $200 to $250 from China via eBay or similar.
For HF and below, both appears to use the LTC2208.... or a clone.... or a salvage chip? The LTC2208 is 15 years old at this point, but AFAIK, it still is not a cheap IC to legitimately source new. Up to 32MHz sampling, with up to 28.8MHz alias-free sampling. USB 3.0 is required for such high sample rates.
BTW, above HF they use a common R820T2, but apparently with up to 8MHz sampling currently possible.
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About software, AFAIK there is a modified version of HDSDR+EXTIO for the RX-666, plus I have seen a claim the BBRF103 project EXTIO should work. I have no idea if either supports configuring the LNA in the RX-888, though.