Hello,
I'm new in the forum (first post here),
I have tried to search before posting but I didn't find something useful.
I'm here to humbly ask for help/advice, if possible.

I have a HP laptop
(Dual core T9400 2,5Ghz, 4GB ram, Nvidia 9600M GT with 512MB dedicated ram, 5400rpm HD,Vista 64 Home Premium with an unknown firewire chip)
and I own a Fireface 400 from several years (but never used with this laptop for 192 kHz work).

Trying to keep the things short,
the issue I refer below is present even using the  laptop in a “heavy” DAW optimized configuration:
background process scheduling on for ASIO optimizing, no system sounds, Aero/visual effects disabled with advanced graphics settings set to classic view and  max performance, no system restore, no disk indexing, no UAC, no apps running (including av/firewall/defender etc), high performance power management, all not needed services stopped (a-la Viper)
All hardware devices not strictly needed disabled (including wifi and wired network, every kind of multimedia device and onboard IDT audio chip)
Vista 64 SP2 full patched, latest Nvidia 285.62 and latest Intel drivers
to avoid emi interference in the working room all the lights were off an no cellphones/wifi or any other kind of device was present or on. Different cabling/positions checked too.
ff400 with firmware 1.70 and 3.062 drivers (2.9992 tested with same results)

The laptop, even if obviously not a speed demon by current standards, is perfectly functioning and very smooth running (in total only 12 processes in idle state).

DPC latency graph show a mean stable constant value of 80-100 microseconds in idle mode or during steady state audio rec/playback,
with occasional peaks to 500-600 microseconds only if launching new apps or things like that.

In this configuration I have no problem to record and playback audio with the ff400 at 24bit/96kHz,
using 128 or 256 samples of latency and limiting bandwith to “Analog+SPdif”.

In addition  I have verified  that I have absolutely no “glitchs” in the file recording a stereo wav from mic ports 1&2 at 24bit/192khz (using digicheck global record and/or third party apps) and using1024 latency (I have not tested lower values).

The big problem is that if I try now to playback the same 24bit/192khz  stereo wav (using digicheck global record and/or third party apps) I get a variable hell of /click/noise/distortion and I notice visible crosstalk in the mixer affecting others playback channels (not only the two used).
Limiting bandwidth to “Analog” only and  increasing latency to the max allowed 2048 value help the things, but does not resolve the issue. I see always “0 errors” in the ff settings panel near latency values.

The (not so) funny thing is that I have verified that if I enable the poor onboard IDT audio chip the same 24/192 file is played perfectly @ 24/192 (tested with third party apps setting a latency of 100ms ? 19200 latency samples @192kHz).

So,
it seems definitely a firewire bandwidth issue, I don't know the onboard chip manufacturer.
But what I cannot easily understand is that:
given that wih my ff400 I can succesfully rec/playback at 24/96 (using only 128 or 256 latency values)
and given that in the same conditions I can successfully record at 24/192 using 1024 latency
why I'm not able to playback the same recorded single stereo 24/192 file even using 2048 latency?

(Note that the poor IDT onboard chip is able to perfectly play the same file @24/192 using 19200 samples of latency).

In my opinion if I'm able to record succesfully something
I should be able to playback it again succesfully with the same settings.
Unlucky, even if difficult to accept, I cannot  test values higher than 2048 because this value is the maximum allowed in the settings menù.

As you can easily understand, I have spent a lot of time/work trying to analyze/troubleshoot this issue, without success.
So now  I kindly ask your opinion/advice/explanation of the observed behaviour.

In addition:
do you know if there is a known workaround to set a latency value higher than 2048 (by manual registry hack or something similar)?
Do you think that maybe buying a firewire Espresscard with TI chipset (I don't know if something similar is available) will solve the issue?

Any suggestion/hint will be highly appreciated.

Thank for the patience (long post)
ciao

alphaomega