The reason I'm not sure is I couldn't find an exact match. Those are the Onkyo codes for the DX-6920 (protocol NEC1, 210.44 with NEC2 for repeat group). But yours is the DX-6990 (same as G10). Usually the codes are the same for such close model numbers. So I'd say I'm 95% confident. And with One-for-all, even if only a few functions work, the others can be added using specific function codes (see the EFCs below).
The problem is very few OFA remotes have that old code, which is why I recommend just the one model remote, which is one of the few still available in the US that has that code. The only European OFAs I know of that have that code are the URC-7780 and URC-7781. I don't know if they're still even on the market.
Otherwise, a cheap Harmony like the 200 or a PC programmable OFA like the Nevo C2 will be your best bet. The Nevo is only about $20 US including worldwide shipping from China. With Harmony, you'd pick the Onkyo DX-6990 from their database. With the Nevo, you'd download the DX-6920 file from hifi-remote.com, assuming the codes are the same (they most likely are).
Here are the function codes (OBC) in decimal if you want to generate the pronto hex using the above protocol info:
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