Thing began to happen after NetBSD 1.5.3 (last tested was 3.99.15). I can't get any sound playing a music cd. But sound works fine when a mp3 file is being played. Sound messages from various softwares(for example kde "ouverture") can also be heard. dmesg is below. Its last lines register what happens when I try to play a music cd. Could someone help? Many thanks in advance. 
 Paulo
(Following "snapshot" is in fact NetBSD 1.6.1 with small modifications on wscons/keymaps and zoneinfo for personal purposes).

NetBSD 1.6.5_AUKAR (GENERIC) #0: Fri Mar 17 10:02:50 BRT 2006
    gnud@makunaima:/mnt/usr/local/obj/sys/arch/i386/compile/GENERIC
cpu0: AMD K6-2 (586-class), 451.06 MHz
cpu0: I-cache 32 KB 32b/line 2-way, D-cache 32 KB 32b/line 2-way
cpu0: features 8021bf<FPU,VME,DE,PSE,TSC,MSR,MCE,CX8>
cpu0: features 8021bf<PGE,MMX>
total memory = 375 MB
avail memory = 341 MB
using 4832 buffers containing 19328 KB of memory
BIOS32 rev. 0 found at 0xfb240
mainbus0 (root)
pci0 at mainbus0 bus 0: configuration mode 1
pci0: i/o space, memory space enabled, rd/line, rd/mult, wr/inv ok
pchb0 at pci0 dev 0 function 0
pchb0: VIA Technologies VT8501 MVP4 System Controller (rev. 0x02)
agp0 at pchb0: aperture at 0xe0000000, size 0x10000000
ppb0 at pci0 dev 1 function 0: VIA Technologies VT8501 CPU-AGP Bridge (rev. 0x00)
pci1 at ppb0 bus 1
pci1: i/o space, memory space enabled
vga1 at pci1 dev 0 function 0: Trident Microsystems product 0x8400 (rev. 0x5b)
wsdisplay0 at vga1 kbdmux 1: console (80x25, vt100 emulation)
wsmux1: connecting to wsdisplay0
pcib0 at pci0 dev 7 function 0
pcib0: VIA Technologies VT82C686A (Apollo KX133) PCI-ISA Bridge (rev. 0x14)
pciide0 at pci0 dev 7 function 1: VIA Technologies VT82C686A (Apollo KX133) ATA66 controller
pciide0: bus-master DMA support present
pciide0: primary channel configured to compatibility mode
wd0 at pciide0 channel 0 drive 0: <ST310212A>
wd0: drive supports 32-sector PIO transfers, LBA addressing
wd0: 9768 MB, 16383 cyl, 16 head, 63 sec, 512 bytes/sect x 20005650 sectors
wd0: 32-bit data port
wd0: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 4 (Ultra/66)
wd1 at pciide0 channel 0 drive 1: <SAMSUNG SP0411N>
wd1: drive supports 16-sector PIO transfers, LBA48 addressing
wd1: 32253 MB, 16383 cyl, 16 head, 63 sec, 512 bytes/sect x 66055248 sectors
wd1: 32-bit data port
wd1: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 5 (Ultra/100)
pciide0: primary channel interrupting at irq 14
wd0(pciide0:0:0): using PIO mode 4, Ultra-DMA mode 4 (Ultra/66) (using DMA data transfers)
wd1(pciide0:0:1): using PIO mode 4, Ultra-DMA mode 4 (Ultra/66) (using DMA data transfers)
pciide0: secondary channel configured to compatibility mode
atapibus0 at pciide0 channel 1: 2 targets
cd0 at atapibus0 drive 1: <ATAPI-CD ROM-DRIVE-56MAX, , Ver 56P> type 5 cdrom removable
cd0: 32-bit data port
cd0: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 2 (Ultra/33)
pciide0: secondary channel interrupting at irq 15
cd0(pciide0:1:1): using PIO mode 4, Ultra-DMA mode 2 (Ultra/33) (using DMA data transfers)
uhci0 at pci0 dev 7 function 2: VIA Technologies VT83C572 USB Controller (rev. 0x06)
uhci0: interrupting at irq 11
usb0 at uhci0: USB revision 1.0
uhub0 at usb0
uhub0: VIA Technologie UHCI root hub, class 9/0, rev 1.00/1.00, addr 1
uhub0: 2 ports with 2 removable, self powered
pchb1 at pci0 dev 7 function 4
pchb1: VIA Technologies VT82C686A SMBus Controller (rev. 0x10)
cmpci0 at pci0 dev 9 function 0: C-Media Electronics Inc CMI8738/C3DX PCI Audio Device (rev. 0x10)
cmpci0: interrupting at irq 10
audio0 at cmpci0: full duplex, mmap, independent
opl at cmpci0 not configured
mpu at cmpci0 not configured
rtk0 at pci0 dev 11 function 0: RealTek 8139 10/100BaseTX
rtk0: interrupting at irq 11
rtk0: Ethernet address 00:e0:7d:92:18:02
ukphy0 at rtk0 phy 7: Generic IEEE 802.3u media interface
ukphy0: OUI 0x000000, model 0x0000, rev. 0
ukphy0: 10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, auto
isa0 at pcib0
com0 at isa0 port 0x3f8-0x3ff irq 4: ns16550a, working fifo
pckbc0 at isa0 port 0x60-0x64
pckbd0 at pckbc0 (kbd slot)
pckbc0: using irq 1 for kbd slot
wskbd0 at pckbd0: console keyboard, using wsdisplay0
lpt0 at isa0 port 0x378-0x37b irq 7
pcppi0 at isa0 port 0x61
midi0 at pcppi0: PC speaker
sysbeep0 at pcppi0
isapnp0 at isa0 port 0x279: ISA Plug 'n Play device support
npx0 at isa0 port 0xf0-0xff: using exception 16
fdc0 at isa0 port 0x3f0-0x3f7 irq 6 drq 2
fd0 at fdc0 drive 0: 1.44MB, 80 cyl, 2 head, 18 sec
isapnp0: no ISA Plug 'n Play devices found
apm0 at mainbus0: Power Management spec V1.2
biomask fb6d netmask fb6d ttymask fbef
Kernelized RAIDframe activated
boot device: wd0
root on wd0a dumps on wd0b
root file system type: ffs
wd0: transfer error, downgrading to Ultra-DMA mode 2
wd0(pciide0:0:0): using PIO mode 4, Ultra-DMA mode 2 (Ultra/33) (using DMA data transfers)
wd1(pciide0:0:1): using PIO mode 4, Ultra-DMA mode 4 (Ultra/66) (using DMA data transfers)
wd0a: error reading fsbn 175584 of 175584-175599 (wd0 bn 11893584; cn 11799 tn 3 sn 3), retrying
wd0: (aborted command, interface CRC error)
wd0: soft error (corrected)
wsdisplay0: screen 1 added (80x25, vt100 emulation)
wsdisplay0: screen 2 added (80x25, vt100 emulation)
wsdisplay0: screen 3 added (80x25, vt100 emulation)
wsdisplay0: screen 4 added (80x25, vt100 emulation)

cd0: no disk label
cd0(pciide0:1:1):  Check Condition on CDB: 0x28 00 00 00 00 00 00 00 01 00
    SENSE KEY:  Illegal Request
     ASC/ASCQ:  Illegal Mode For This Track

cd0: dos partition I/O error
cd0(pciide0:1:1):  Check Condition on CDB: 0x43 00 00 00 00 00 00 00 04 00
    SENSE KEY:  Not Ready
     ASC/ASCQ:  Medium Not Present