CentOS - Jul 2014 - CentOS6: sound prefs, how to limit output volume to the un-amplified range?

Hello there,

recently installed CentOS6 on a (quite old) 64-bit system, and from the
GNOME's sound preference app, I can see that the Output volume range is
said "amplified" from 63% to 100%. Below 63% it's unamplified.

No idea what's implied behind this amplification (I don't see this on
other desktops), but I notice that when "amplified" the sound is
pretty
bad (at 100% and above, it's ridiculously bad). Below 63% it's simply
very good and from far, loud enough.

I wonder if there's a way to make the amplified range (63-100+)
inaccessible? It makes no sense to me to allow the amplified range if
it sounds bad (tested with different external speakers).

lspci says, about the device:

00:14.5 Multimedia audio controller: Advanced Micro Devices, Inc. [AMD/ATI] IXP
SB400 AC'97 Audio Controller (rev 02)
        Subsystem: Hewlett-Packard Company Device 2a2f
        Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr-
Stepping- SERR- FastB2B- DisINTx-
        Status: Cap+ 66MHz+ UDF- FastB2B- ParErr- DEVSEL=slow >TAbort-
<TAbort- <MAbort- >SERR- <PERR- INTx-
        Latency: 64 (500ns min), Cache Line Size: 32 bytes
        Interrupt: pin B routed to IRQ 17
        Region 0: Memory at fe02a000 (32-bit, non-prefetchable) [size=256]
        Capabilities: [40] MSI: Enable- Count=1/1 Maskable- 64bit-
                Address: 00000000  Data: 0000
        Kernel driver in use: ATI IXP AC97 controller
        Kernel modules: snd-atiixp

More info about this sound config from alsa-info:
 http://www.alsa-project.org/db/?f=0d3c6aa7d09515bb9499c97e977ff8988ea8a4cb

Regards,

-- 
wwp
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