Gryphon’s site mentions “In 1998, The Gryphon CDP-1 CD player introduced the world to the sonic improvements offered by 88.2 kHz asynchronous sample rate conversion, the world’s first implementation of this advanced technology, now ubiquitous in digital audio.”
The PCM1704K upsampling chip came out in 1998 (I think, at least there are datasheets from then). Theta and Wadia used it in their players then. SimAudio a little later.
Tho it might be a matter of semantics, asynchronous upsampling is different from upsampling the way I think you mean it. The PCM1704K did 8x oversampling with a 96k input which is probably more like what you were talking about.
At WaveFrame (where I met Gus) we were using sigma delta converters from Crystal Semiconductor which upsample in digital audio workstation products in '87 - '88. We also offered asynchronous sample rate conversion to go from 44100 to 44055.9 and vice versa then too.
I’m sure there were a lot of others in that same timeframe.