I'd think you could use any that works with alloy engines. But, the
cooling system is not really a big problem area on our cars (couple
of minor problems). So, if you use Volvo coolant you are using
something that is working well in thousands of Volvo cars. I'd use
the Volvo coolant.

The possible problem areas are the radiator reservoir cap and thermostat.
The gray reservoir caps can leak a bit keeping the system from reaching
full pressure. There is a newer teal/green/blue colored cap (depends
on who you ask) that is an improved design.

The thermostats seem to need replacing about 70K miles. I have a 95 with
65K and the thermostat is OK. My 98 with 55K miles currently has a
failed thermostat (car runs cool). You might keep an eye on this.
Replacement instructions are at http://volvospeed.com/bay13.htm.