I cross-checked with the response from Acer on Acer's site, and it appears that this machine can
recognise 16 GB, despite the spec listed on Acer's site. Sorry.
In regard to mixing RAM sizes, you have 4 slots; channel A is slot 0 and 1; channel B is slot 2 and 3. Since you have dual channel support, keep the same sizes for each channel, and you should be fine.