Multiple Criteria's

Try:

=IFERROR((SUMPRODUCT((('3-Service Calculator'!$G$1:$G$10000="7-part call")+('3-Service Calculator'!$G$1:$G$10000="8-high part")),--('3-Service Calculator'!$X$1:$X$10000=1),'3-Service Calculator'!$S$1:$S$10000)/SUMPRODUCT((('3-Service Calculator'!$G$1:$G$10000="7-part call")+('3-Service Calculator'!$G$1:$G$10000="8-high part")),--('3-Service Calculator'!$X$1:$X$10000=1)))/24,0)

Also note, that SUMPRODUCT is less efficient than AVERAGEIFS so try to limit the range sizes to the absolute largest you will need... a range of 1:10000 may cause performance issues if you have many of them.

Edit: You can possibly also just add 5 different AVERAGEIFS together, one for each Grange value (keeping the X and S ranges in tact in each). and then divide the entire thing by 24