We have tested the PCL-858 with the following configuration:

PCA-6751	CPU: PII 266 MHz
		RAM: 64Mb
PCA-6653 	+ CRT
PCL-858
OS: WinNT 4.0 + SP5.0

We found that the PCL-858 can work well with or without PCA-6653. Following is our test steps:

1, We test the PCL-858 with only PCA-6751 first. 
Before starting WinNT, please make sure the IRQ you assign to PCL-858 is available. From the manual of PCA-6751, you can find the IRQ10 is available. However, since the on board net card is PNP, some time the net card will occupy the IRQ10. To make sure the IRQ10 is reserved for PCL-858, you can make some modification in the BIOS setting. After entering the BIOS setup window, you can find the setting in : 'PNP/PCI CONFIGURATION' =>  set 'Resources controlled by:' to 'Manual' => change 'IRQ-10 assigned to :' to 'Legacy ISA'.
Then the IRQ10 will not be used by any PNP device.

2, Enter WinNT install the ports on the PCL-858 as Com3 to Com10. There are something we should notice:
	a, The JP3 on PCL-858 should be set on the right position
	b, Enable the share IRQ function in WinNT system. You can find the detail steps about how to enable it by referring 		     the database 'FAQ98BA06'.
	c, During our test, the setting of PCL-858 is : base address 300H, Vector address 200H, IRQ10, Low speed mode.
	d, We can install the ports with our ICOM utility or install all of them one by one just like the steps in 'FAQ98BA06'.

3, Test the Com port of PCL-858. We connect the Com3 to Com4, and test them with a Windows test program 'Commtest'. Attached file is the program. Or you can test them with 'hyper terminal'.

4, After ensuring the PCL-858 is workable with PCA-6751. We turn the power off, plug the PCA-6653 then restart the WinNT. We found the PCL-858 can still work well when we repeat the step3.

After the test above, we believe the PCL-858 should be workable with PCA-6751 and PCA-6653. Would you please follow the steps and check it again? If you have any further question, please tell me and I will check it right away.

By the way, sorry that there is one mistake in my last reply, from the manual, the PCA-6653 will not use the IRQ10.