External Buffered FX Loop Box

[Hugh Jazz]

I just bought a Mesa Express 5:25 combo amp.  It's a fantastic-sounding amp and would be perfect for me but for one thing--the FX Loop arrangement is, well, bizarre.  It is a series loop, and the FX Send is unbuffered and between the Master Volume and Phase Inverter, so it's sending out a line-level signal that will fluctuate based on how the MV is set.  The Return appears to be buffered by 1/2 of a 12AX7 and expects to receive a line-level signal from the effects.  The manual states that the loop is designed for Line-Level, Pro-Quality Rackmount FX processors only and makes it clear that a careful dance will take place between the MV level and the FX input Level.  Like 95% of modern guitarists, I use pedals and not line-level digital fx units.  Also, even if I did use a rackmount Line-Level unit, since the send is unbuffered, that puppy would have to be about 6" from the Send to avoid signal loss.  I assume the implementation of this FX loop was due to the fact that Randall had 1/2 of a 12AX7 left over and had to figure out what to do with it???  Again, it is perfect in every other way, so I don't mean to disparage the amp.     

Since I depend on an FX loop for my pedals, what I'd like to do is build a little box with two buffers, and I'm looking for some suggestions and advice as follows:

1.  The first buffer would go between the FX Loop Send jack and my Pedalboard's input, so it would need to receive a Line-Level Signal and Impedance from the tube preamp and then Send out an Instrument-Level signal with low impedance to the pedalboard.  What should I use--JFet, Mosfet, OpAmp?  What should the buffer's input and output impedance be?

2.  The Second Buffer would go between the pedalboard output and the FX Loop return jack, so it would need to receive an instrument-level signal from the stomp boxes and send out a line-level signal to the FX Loop return jack.  Again, the FX Loop return is buffered in the Mesa, but it expects to see a Line-Level signal.  Same questions--what should I use--Jfet, Mosfet, OpAmp, etc, and what should the second buffer's input and output impedance be? 

I'm obviously trying to get as clean and transparent an FX loop as possible with unity gain.  Thanks so much for the help!
James