Check you r account again. I did and mine shows the 6.610 software:
998c SI(Version 6.610)
Release Date: 03/15/2013
Description:
v6.610 includes changes to POS Script Updates and includes general performance and stability updates plus everything included in v6.600
Added enhancements for 2D/DI/SI sonar scroll rate on the 798ci HD SI.
Fixed an issue where SI data was scrolling at twice the intended rate.
Fixed an issue where 2D/DI data was not in sync on the 798ci HD SI.
Fixed an issue where 2D/DI data was not in sync if 83/200 kHz mode was enabled.
Fixed an issue where DI Zoom was not in sync.
Fixed SI Sensitivity issues on the 898c SI, 998c SI, 1197c SI, 1198c SI.
Fixed an issue where Demonstration Mode OFF would not force normal mode and a connected transducer state.
Fixed an issue where rapidly forcing the unit into Simulator Mode could cause the unit to restart.
Fixed an issue where Ethernet sonar subscriptions would eventually drop off if the Control Head was booted with Sonar turned Off
Fixed an issue where Ethernet sonar subscriptions would eventually drop off if Sonar was turned Off and then back On within 60 seconds without a reboot.
Fixed an Ethernet issue where the Heading Line ON/OFF setting would not be saved between restarts while subscribed to a remote AS GPS + HS.
Removed Universal Sonar II transducer selection option, now users should select dual beam as their selection.
LakeMaster map coding was updated to work with i-PilotLINK
Tweaks were made to radar functionality to fix a memory leak
Fixed a bug that caused some models to sometimes skip a view when cycling through views.
Locked NMEA output at 4800 baud when enabled
Added 360 Imaging operation menus and capabilities
Added iPilotLINK operation menus and capabilities