x3
Yep, use an XP-9-20 transducer along with the AS-Si-DB-Y cable and you should be able to get high-speed depth readings.
"Professionally installed" just means that you paid someone to do it. If they knew what they were doing they should have told you that you would not get dpeth readings at high boat speeds as that area would be out of the water. Make sure that whoever installs the XP-9-20 does the on-water testing or it may not work correctly.