The GUS MAX troubles

I have such a problem:
A Gravis Ultrasound (MAX 2.1) card + RH Linux 6.1 (2.2.12-20) I load the drivers as described in /usr/src/linux/Documentation/ultrasound:
modprobe sound
insmod ad1848
insmod gus io=0x220 irq dma=1 gus16=1 type=0 dma16=5

so I get normally working devices:
the PCM playback/record (/dev/dsp)
/dev/dsp1 (2nd playback/record)
and
/dev/mixer
/dev/mixer1 (looks like second mixer)
and some other:
/dev/audio & /dev/audio1 - seems to be equal to dsp /dev/sequencer and /dev/midi0[0-3] - seem to be something around midi :)
- theese are not used (now)
but:
the /dev/dsp and /dev/dsp1 cannot work simultaneously:
neither two plays, nor Full Duplex (one to play,another to record) -though I've specified _two_ DMA channels, the second one is 16bit (as it is said in docs)
there are no other ISA cards in a box (the 5Ali61 motherboard i.e. Alladin IV chipset)

can someone help me
or point the places on the WWW where I can read about GUS and it's use under Linux??

Hope world will help
Sergey