A guru is someone that already know what's doing, i'm only learning and doing tests to made this product a bit better without spending too much. A good function generator costs too much for me, and i prefer to increase my knowhow a bit...
Someone with good skills can do all this in few minutes
In the meantime i was searching other triple analog muxes with ron<5ohm, and the only ones seem adg1633, adg1433 (almost identical, with different bandwidth) and the pin to pin compatible adg733. The first two have 4ohm Ron, the supply can be unchanged (works with +5/-5v), but the pinout is a lot different, and not seem pratical the conversion.
The adg733 is almost compatible, but it have a suggested supply of +2.5/-2.5v. This is not good as the control lines from the altera chip are 3.3v and the digital lines allow a maximum of vcc+0.3v (so 2.8v), so at least the +v must be +3.0v (but we have already a 3.3v regulator so i'm using it), giving a total voltage of 5.8v, a bit out the reccomended 5.5v max but a lot less than the absolute maximum limit of 7v.
The things to do for have it working in the signal generator is lift the +vcc pin and connect it to the +3.3 voltage regulator (including coupling capacitor), change the onboard -5v voltage regulator to a -2.5v one (the -5v seem used only by the analog switches), change the feedback resistor of the opamp after the dac for have a max 5vpp (better a bit less) signal instead of the near original 7.5vpp, and change the gain of the power output opamp. the 2.5ohm ron resistance of the adg733 vs the 50~80ohm ron of the 4053 will increase a lot the accuracy of the amplitude setting. if it's not enough, it's possible to increase the value of the r-2r attenuation network.
The big question about all this mods is the output filter, i not know almost nothing about filter design
Plus at least one hundred of things that for sure i'm missing as i have no experience in this field... But i want to learn