I have owned a C3500 for a week now, before I had an S3000 since November 2015, so yesterday at my first gig with the C3500 I noticed two things:
a)
EQ:
the width button should be lockable, so you don’t always need two hands.
please!
b)
Double FX display?
if you selected the FX window on the right and press SEL to call up an effect, then this effect appears on both screens.
For the desks with one screen this is practical if the effect is on the left (on one screen), but for desks with double screens it is not a practical solution.
It would therefore be good if the software recognizes that there is a second screen and then leaves the left screen unchanged when an effect is selected via SEL. Please note: of course only if the FX window on the right is selected!
These two things I would wish for a better workflow.
Thanks 
after some gigs in the last months with my new C3500 I would like to point out once again that I wish us on the EQ a possibility to determine the button for the EQ bandwidth.
So not toggle, but switch between bandwidth and frequency.
as described above under a).
At the moment you always need two hands to operate it, but if you hold the talkback microphone in the other hand, you reach the limits of operability too quickly.
and the implementation of point b) would be just as nice.
and what really amazes me is that I miss the potentiometer for the LoCut compared to the S-series. Sure, you can also put this on the potis under the strips, but there I usually switched the PAN.
otherwise i think this console is really good, it fits my requirements best. the purchase was a good choice.
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I second the point a
I have a C2500 so b is not relevant to me
some more funktionality for the LC assigned to the rotaries would be helpful,
an indication that the LC is on or off and not only the frequency
and maybe the HC in the same manner available on the rotaries,
and gate threshold?
right, I had already requested gate threshold in 2015.
that would be of much more use to me personally than the threshold-function for the compressors, which is already available from the beginning.
and a display on the rotarys, which locuts or hicuts are included, would be quite interesting. but you can’t switch them on or off on the rotarys at all… hmmm.
LC and HC on/off should be available from the EQ page. Also, highlighting the LC/HC band from the EQ page should put the Frequency on the TnT knob. To me this seems like a brainfart more than anything else - as a feature starvation choice it would be simply stupid.
EQ:
the width button should be lockable, so you don’t always need two hands.
please!
please!!
please!!!
+1 for latching mode on PEQ Width button.