Could be something specific to the print server. Without knowing how it works it is difficult to provide help.

I must ask this question again: "Is there any chance of starting the printing only if the complete output is processed for printing??" In an article I found in the internet (I can't find it again) someone mentioned that printing would be faster if the data-transfer to the printer starts only if all data for printing have been processed. Wich process does the spooling and which process "does" the data-transfer to the printer???

I have some data about the print server and you can find them here:

This page displays the current system settings of the print server.

System Information
Device Name : PSD5A0FA Raw Printing : Enable
Printer Server Name : ML1210 IPP Printing : Enable
Model Type : 1P-PS LPR Printing : Enable
Firmware Version : 3.4.21 AppleTalk Printing : Enable
MAC Address : 00:00:B45:A0:FA NetWare Printing : Enable
USB Port Number : No SMB : Enable
LPT Port Number : 1 SNMP : Enable
Wireless Lan Status : No NetBEUI : Enable

This page displays the information of each printer connected to the print server.

Note: if your printer does not support bi-directional function, some information will not be displayed correctly.
Printer 1
Manufacturer :
Model Number :
Printing Language Supported :
Current Status : Off_line

This page displays the current TCP/IP settings of the print server.

TCP/IP Settings
Use DHCP/BOOTP : Off
IP Address : 192.168.1.111
Subnet Mask : 255.255.255.0
Gateway : 192.168.1.1
Use DHCP Server : Off

This page displays the current SMB settings of the print server.

SMB Settings
SMB function : Enable
SMB Group Name : MSHEIMNETZ
Pass Job When Error Occured : Enable
Waiting time to pass job : 20 SEC

Data about SNMP, NetWare and AppleTalk are as well available but I don't think we'll need them.