What is the best way to upgrade your video surveillance infrastructure?

Question

CCTV

Hello.
There are the following: 80 offices in the city. Most of them have D-LINK DCS-2210 cameras.
Until recently, everything was fine, but it became necessary to listen to the office.
With an abundance of solutions - confused.
Solution 1) purchase new cameras with microphone inputs and microphones for them, such as Rustle. The issue price is about 10,000 rubles. (DCS-3010) Or, alternatively, a "non-domestic" camera, like this: Proline IP-HD356IRP + microphone. The issue price is about 5000 rubles.
Solution 2) Tame USB microphones and somehow collective farm. Those. leave our cameras and somehow synchronize the microphones.
It is clear that the first option is categorically more expensive, but everything seems to work "out of the box"
The second option is preferable, but what are the costs (time / money) for implementation?
Maybe there are other options?