those figures tell you nothing without knowing what level a sample is playing at, it's SNR that's important, a ratio rather than an absolute value. Lastly if you had set everything up correctly for the test a noise floor of almost -60dB is actually very good for an 8-bit sampler.
There is something being missed here.... Don't forget by the time anything is sampled in EII, regardless of whether it's via the sample in (which is a shame not to use as it's a large chunk of EII's character thanks to it's discrete successive comparative convertor which actually uses one of the output channels to generate the sample comparator sawtooth!!) or the host PC interface, the sound has to pass through analog filters and VCAs - this will have the effect of dramatically improving the SNR.
The PSU's in the EII are notoriously bad - it may be that a duff PSU and possibly some bad tantalum caps are resulting in fact more noise from the digital stages finding their way into the audio path.
A Word of Warning.... I strongly urge anyone who values their EII to have the now 30 year old PSUs checked over by an engineer and recapped as they have a very bad habit of going bang and taking all sorts of circuitry with them. I also recommend fitting a low noise fan to one side of the PSU (some were factory fitted).
As luck would have it, I've been rearranging my studio this weekend and got to dust off my monster for a quick test recording... I'd actually forgotten how nice it sounds!
I recently recapped this beast and fitted a superb HxC Floppy Disk Emulator - so no more flakey 5.25" disks... it realiably loads/saves from SDcards
Recorded from the mix output directly via an old but quite sweet sounding Roland SRX-330 reverb - no EQ, compression or noise gate.
I have left the final couple of seconds of silence unmuted to demonstrate a typical noise level which I really don't think is that bad for such a monstrously complex classic digital hybrid beast.