It appears that the HK amp is more than an amp. It takes left and right channel inputs and mixes/equalizes them to the eight speakers (marketed as 12 by counting mids and highs separately.)
Control of the equalizer appears to be in the factory audio/nav HU. Thus, it all goes away with an aftermarket HU.
Inputs
(i262) No. 1 MUTE MUTE
(i262) No. 2 L– Left channel negative input
(i262) No. 3 L+ Left channel positive input
(i262) No. 4 R– Right channel negative input
(i262) No. 5 R+ Right channel positive input
(i262) No. 6 SLD Shield
(i262) No. 7 TX– Transmitter negative
(i262) No. 8 TX+ Transmitter positive
(i262) No. 9 EQ CHG Equalizer select (change)*1
(i262) No. 10 L/RHD-SEL Equalizer select (change)*2
(i262) No. 11 SPEED Vehicle speed pulse
(i262) No. 12 ACC ACC power supply
(i262) No. 13 NC Not connected
(i262) No. 14 II1– Interrupt information negative
(i262) No. 15 II1+ Interrupt information positive
(i262) No. 16 NC Not connected
(i262) No. 17 NC Not connected
(i262) No. 18 SLD2 Shield
(i262) No. 19 NC Not connected
(i262) No. 20 NC Not connected
(i262) No. 21 NMUTE Navigation mute (not used)
(i262) No. 22 NC Not connected
(i262) No. 23 NC Not connected
(i262) No. 24 TMUTE Telephone mute (not used)
Outputs
(B316) No. 1 +B Battery power supply
(B316) No. 2 NC Not connected
(B316) No. 3 NC Not connected
(B316) No. 4 NC Not connected
(B316) No. 5 NC Not connected
(B316) No. 6 NC Not connected
(B316) No. 7 NC Not connected
(B316) No. 8 WF+ Sub woofer positive
(B316) No. 9 TWR+ Instrument panel right side speaker positive
(B316) No. 10 CTR+ Instrument panel center speaker positive
(B316) No. 11 FL+ Left side front door speaker positive
(B316) No. 12 FR+ Right side front door speaker positive
(B316) No. 13 TWL+ Instrument panel left side speaker positive
(B316) No. 14 RL+ Left side rear door speaker positive
(B316) No. 15 RR+ Right side rear door speaker positive
(B316) No. 16 +B2 Battery power supply
(B316) No. 17 NC Not connected
(B316) No. 18 GND2 Ground
(B316) No. 19 NC Not connected
(B316) No. 20 NC Not connected
(B316) No. 21 NC Not connected
(B316) No. 22 NC Not connected
(B316) No. 23 WF– Sub woofer negative
(B316) No. 24 TWR– Instrument panel right side speaker negative
(B316) No. 25 CTR– Instrument panel center speaker negative
(B316) No. 26 FL– Left side front door speaker negative
(B316) No. 25 FR– Right side front door speaker negative
(B316) No. 28 TWL– Instrument panel left side speaker negative
(B316) No. 29 RL– Left side rear door speaker negative
(B316) No. 30 RR– Right side rear door speaker negative