Diki, I have done exactly that..I run the E-60 into the Audio inputs on the G70..and listen from the G70 headphones or out put to sound system..

The classic piano is the closest to the Grand X [so close I can't tell the difference]..and yes the filter can brighten the classic piano more...

I turn all effects off , including keyboard and master effects..and I balance the volume levels of the E and G...
The dynamics from each keybed is very similar too..

I originally thought[last year] that the sounds were different[from on line demos]..but, now I believe they are the same...even the blow alto vib and jazz scat are identical..

I searched to see how large the wav memory is, but can't find it anywhere..

I think that the E-60 is more keyboard than I and many others thought it would be..

The built quality is nothing like the EXR series..in fact I think it may be better built than the VA series[VA-7]..

As I mentioned earlier..what is missing from the G-70:

The keys are less weighted, but still fun to play.

No vocal input or harmonizer..

one less lower and upper tone selections..

No audio inputs..

No mastering effects other than bass enhancement for speakers..

No color screen[16 gray shades]..

Smaller internal memory [17mgs].

Also no separate part eq..

And the E-70 lost 18 pounds somewhere..

If someone stole both my G70 and my E-60...the first board I would replace first, would be the G70, because we must remember, all these great features are comparing to the G70..and true to form the G70 is better..

But , If I was in no need of a mic input/harmonizer, and audio inputs...The E-60 makes every bit of sense..You have all the Covers, and all the sequencing power too and reads the G70 data from the G70 card..even from my 1 gig card..