Hard to be certain as there are, often, surprising variabilities among different equipment but, in general, yes.
Only if the line preamp has a true Tape monitor function. That is, when a source is selected and sent to the tape record out, selecting tape monitor substitutes the Tape In for the selected source without disconnecting the source from Tape Rec Out.
In the 80's, this was common to every pre-amp, integrated amp. Today, it is rare.
My Halo P3, for example, has Tape Rec Out/Tape Play In, but if you select "Tape" you can only get an input from the tape Play In and the record source is disconnected.
However, the P3 gets around this by having an "External Processor" loop, which is effectively a place to splice in an external device between the source and the volume gain control sections of the pre-amp.
The obvious alternative is to put your EQ between your Line amp outs and your Power amp inputs. If it's got a gain of 1, should be no issue.
I might get me an integrated tube amp without tone controllers, which my current have, and sometimes I really need those. I might get a Jadis DA 60. Here are some pics of a similar one. http://www.ls3-5a-forum.com/phpBB3/viewtopic.php?t=2662
I still don't know for sure if it would work with an eq connected to an amplifier like this, but I think so.
The obvious alternative is to put your EQ between your Line amp outs and your Power amp inputs. If it’s got a gain of 1, should be no issue.
It is an issue when you have 6 channels going out and several power amps.
I am trying to run eq and compressor limiter as egoben asked about utilizing two or more sources. I am going to try using the tape monitor functions and those connections.