Hello again, i kinda feel bad to post another topic about a different laptop model this time compared to my last thread being about a Latitude E6420. But i have another laptop with a slightly different problem I can not ever figure out, and this time it's reguarding the Audio/Sound on a Dell Precision M6400.
I started with a clean fresh install of XP SP3, and things were going okay. I started doing the drivers slowly, starting with the chipsets, PCM cards, audio, video etc -- until i noticed something was really "off" about the way the audio sounds. First it's "IDT IDT 92HDxxx HD" It's really hard for me to explain this in words but i'll try. 
For example when i double-click the audio icon in the system tray normally to bring up the volume control window, and just simply click the slider ..it sounds horribly low quality..washed out, "muffled" ..something like that. I dont know the right word to describe it. but if i click it really rapid and fast, it actually sounds normal like it should ...but if i slow down how fast im clicking it, it'll instantly be back to really bad.
It's as if it's going into some sort of power saving mode instantly or...really low/bad "sample quality rate" or...something. Instead of staying normal. The weird thing is, if i open any of my gaming emulators..or youtube or something that relies on sound whatsoever, it'll always be back to normal, but the second i close anything, it's back to crap. Thats why it's so hard for me to explain. I've never experienced such a thing happen on my D620, or the E6420 laptops...and never on any past PC's from the 2000's (win XP only)
I've seriously checked and tried everything i possibly could so far. I went to the IDT control panel and disabled the "power management" option and all the others there. - i went to the "andrea filter" control panel which has only 4 different settings, tried all of those - no difference --
https://youtube.com/watch?v=cQbK9q_IQDs
i tried the method in this youtube video i saw about disabling the ESata Port in the BIOS ...which apparently fixed it for hundreds of people...i saw a comment or two of people doing this for the M6400...i guess it's a fix for Win 7 and 10 only.
I tried disabling a few other things in BIOS like wifi, lan/ethernet, all the media cards - tried disabling a bunch of other things 1-by-1 in windows device manager, dvd drive, even the "microsoft UAA sound driver" thing which only just disabled the sound entirly ...but turning back on didn't help.
I tried each and EVERY single version avaiable of the IDT from here:
https://www.dell.com/support/home/en-us/product-support/product/precision-m6400/drivers
A01, A03, A05, and A06 ...the bad news is that every step UP only makes it worse....only A01 is the closest possible thing to getting it to fixing it.
I also tried a driver that was meant for E6410/E6510 and M4500/6500 ..which managed to install but didnt help.
I then tried the current driver version that was on my E6420 laptop because it's IDT also ..but it wouldnt install because it'd say "your hardware ID is not compatible with this version"
I double-checked with the Direct X diagnostics tool - start -> run -> dxdiag -> sound tab and checking all the options on the slider for Hardware acceleration -- and i double-checked the 2 slider buttons for the Sound/Audio Devices Control panel going to the Advanced tab --> performance and trying out each possible option on "Hardware acceleration" and "Sample Rate Conversion Quality" - no difference on every slider option.
I dont know what else to do. Again basically it's like the audio somehow is getting instantly put into some sort of super low quality bit rate or...power saving..or something i dont freaking know. It's never happened on other laptops or PC's before.
I've read windows 7 and 10 has it's own generic "high defintion audio" driver that can be loaded without needing the IDT's own driver at all and i've been frantically google searching for hours to find out if there's anything like that for XP too but havent had any luck finding such a thing. Is there any ??