Hello and welcome to the forums.
Thats quite old hardware so there are only a few people that know these old stuff at all
At first look you use quite aggressive ram timings.
That can be ok but ram timings are tied to the interleave settings.
So try to alter your ram timings then you should be able to set it to 8 way.
From the official manual:
[FONT=sans-serif]DRAM Bank Interleave[/FONT]
[FONT=sans-serif]Use this option to select DRAM Bank Interleave. Configuration options:[/FONT]
[FONT=sans-serif][Auto], [Disabled], [2-Way], [4-Way], and [8-Way]. The default value is set[/FONT]
to [Auto] to set the timing by dram SPD