I don't really understand what "
shielded freewire points" are ?
And I still don't get why you want to put a 'Chassis Pour' on a pcb ?
An 'AGND pour' will attenuate crosstalk between channels. As will any Copper area held at a low impedance fixed potential eg a voltage rail - but 0V is usually easily available and offers other electrical benefits.
Is it actually a problem in itselfd to have AGND opposite CHASSIS GND ?
Well. as always, it depends...
Assuming you have a double sided 'standard' FR4 1.6mm PCB then you are forming a capacitor with 1.6mm of FR4 as the dielectric. The value of the capacitor will depend on the exact geometries of the copper pour areas.
By my calculation 1 cm sq areas at 1.6mm spacing will give approx 2.5pF ( I am assuming FR4 has permittivity similar to the range given for Epoxy Glass @ 4.2 - 4.7 -ref EMC for Product Designers (Tim Williams) ).
Welcome to check my maths (note it's maths btw
- If I were doing this for money I'd be triple checking it !
So you can take it from there.
The capacitance is relatively small but it does mean that you are getting progressively less impedance between the two planes as frequency increases. It may not seem relevant at anywhere near audioland. But the chassis is subject to the whole frequency range and you want to be shunting that away - not giving it a chance to 'jump' over to your AGND via capacitance (let alone produce EM fields inside the equipment).
There is a case for rf filtering the signal to Chassis but this is best done as near the physical input connector as possible.
Whether or not it matters in reality depends on too many things to think about. But as a general rule - where multiple Ground / Power Planes are used on the same PCB layer and separation is desired a common distance to start at is 3mm. (It's a difficult situation to quantify as the dielectric in that case can be considered to be made up of air / solder resist / FR4 - Good Luck with that
I say - keep CHASSIS on the chassis