very strange problem with audio recording level in capture

[crespo80]

i use a lifeview prime30 PCI card to capture (based on Philps SAA7130 chip) and the program FLY2000TV 2.36.
The card hasn't an audio chip, so i use the chip integrated in my asus p4p800-e deluxe (realtek ALC850).
I plug to line-in connector.
1) the level of volume is very high (but with no distorsions), so i have to set it to the minimum
2) the level of recording volume is influenced by the adjustment of volume made with the control of the speakers!!!! That's incredible. My speakers are the creative 5300 5.1.
I also made a test recording just the audio in cooledit pro 2 and, monitoring the recording level in real-time:
I found the same problem.
If i turn the grip handle of the speakers to lower volume, than the recording levels decreases, if i turn the handle to higher volume, the recording level increases (and can introduce distorsions). If i turn off the speakers there is no recording level!!
The speakers are correctly plugged into their respective outputs (black for rear L/R, yellow for SUB/CENT and green for front L/R) and the line-in to blue connector

HELP!!!

i installed winXP SP2 just few days ago, so the system is clean, the rest of my computer is in signature, and all the drivers are updated to last versions.

[Kalicrys]

Here are a few guesses, I hope they help:

1)
Probably cause of different resistance(ohms)- you know how the output for audio speakers and earphones are different. In my case, I get proper scaling by setting the volume to 20%.

2)
Might be feedback from your speakers back to the sound chip.
Have you tried capturing with the speakers disconnected?