The USB Sound Blasters always had sub-par EAX support, back when the hardware supported it, because they just weren't the same as the internal hardware and couldn't do it as well/quickly. That being said, the early 2000's Sound Blaster USB units did support it and like the newer models with no EAX, do use Creative ALchemy to restore EAX audio to older games, under the newer Windows OS.

Extigy, Sound Blaster Live 24-bit External, Sound Blaster MP3+, Audigy NX, X-Fi HD, X-Fi Go Pro, etc.

All of them support some level of EAX, increasing over the generations, but yeah I think it was always processed on the CPU.

The older models had hardware EAX to a certain degree, but USB audio wasn't something that worked right back then and it had issues due to hardware and software implementations of USB 2.0 being all over the place and often sub-par in terms of speed/performance/latency/stability. Everything after the X-Fi - the last SoundBlaster product line made for Windows XP and the last SoundBlaster product to implement EAX in the DSP - had software EAX-2-OpenAL via Alchemy and all the older products that had EAX functionality use that to this day, to provide EAX functionality by converting EAX calls to OpenAL.

The sound blaster omni too, has eax support.

I'm still using my 16-year-old Creative Labs SB0490 Sound Blaster Live! 24-bit External on my Windows 10 PC.