Help! Power question

As Cleeds alluded to, it may be helpful to indicate which specific Furman model you are using.

And if it is one of their models which provides "current reserve" at some of its outlets, that are intended for connection to amplifiers and subwoofers, a simple experiment that may be worthwhile would be to plug the computer into one of those specific outlets, if you are not already doing so.

It seems possible that when the a/c kicks on a brief dropdown in the AC voltage is just affecting the computer, and the resulting effect on its output is what is causing the DAC to freeze. And if so perhaps connecting the computer to one of the outlets providing "current reserve" would help.

Another possibility that I wouldn’t rule out at this point, btw, is that if the audio system and the a/c unit happen to be located within a short distance of each other, for example if the a/c unit is near a window of the room in which the system is located, airborne RFI that is generated when the a/c kicks on may be affecting the computer through the air. Perhaps as a result of being picked up by the cables or power cord that are connected to the computer. In which case trying a different computer may be worthwhile, if that is practicable. And for that matter, trying a different computer may be a worthwhile experiment in any event, if my first suggestion and the suggestions by the others don’t help.

Regards,
-- Al

A 5 ton unit can have over 100 amp inrush current on startup. Start kit ( capacitor and potential relay) will smooth that out. 

Did you go back with same btu on air conditioning unit?

Agree with acman3 and ghosthouse. The service factor on startup may be causing a temporary drop in voltage. Logic circuits usually use a 5VDC supply. You may be able to get as low as 4.5VDC and still be safe. 115VAC through a step down transformer to yield 4.5VAC is a 25x reduction in voltage. If the line voltage dips to 100VAC, the voltage on the secondary side will drop to 4VAC. Rectification has little to no affect on voltage. At 4VDC the logic circuit would likely freeze and not function until a complete reset of the logic circuit is performed. 

220VAC supplied circuits will use both legs of the service being supplied. Startup will affect all service since the 220 breaker uses both supplied phases. You said when the air kicks on. Not sure where you are located but here in TN we haven’t used the air in months. Is this a heat pump in heat mode?  

You may be able to prove this by testing using a uninterruptible power supply/battery backup unit like used on computers.   This should keep the line voltage stable. 

Just a thought. 

The start of the condenser is causing a whole house voltage drop. I’ve seen this and I’m wondering if the wires leading to the condenser are undersized. You only need a 200 amp service panel if you have a larger home( over 3500sq/ft). 
A/c units normally draw about 25amps during start up that’s why you have a 30 amp breaker connected to it. I would have an electrician check out the work that was done. He/she will find out what’s going on very quickly. 
Giid luck!