To use a preamp with my Line Magnetic 805 integrated amp, or not?

Just a quick update here. I did work with Don to get the preamp fixed and this was sent back to me to try with my Line Magnetic. After about a week of extensive listening, I struggled to hear a big difference between using the preamp on the pre-in vs just having the source go directly into the LM. It didn't make it sound any worse but it wasn't the large improvement I had hoped for. I can only think that the reason for this is due to the Line Magnetic's configuration where the preamp is not bypassed even when using the pre-in input. That is likely the limiting factor. 

Will it be any different if I used another preamp? Not sure. But I know that the Don Sach's didn't have the effect that I wanted to hear unfortunately. Don is a great guy to work with though! Maybe in the future I will go for his pre and amp combo but for now, I'll be returning his preamp. 

If the pre-in input does not bypass the LM's preamp circuitry, I doubt any external preamp will improve the sound through that input.  Does the LM have a tape input?  That bypasses the line circuitry in a number of preamps I'm aware of.  If it does, try that input.

I’ve tried a few different preamps with my LM-508ia, including LTA mircrozotl preamplifier. The preamp that made the biggest difference was when I inserted the Coda 07x linestage in my system. Amazing combo. 

I've only tried one preamp with my LM805ia and that's the VAC Renaissance MKV.  Pretty substantial improvement over running the LM as an integrated.  I really was hoping that I didn't hear a huge difference because I could have sold my VAC and been many dollars ahead, but alas the VAC just adds so much to the clarity, size, and depth of soundstage - it can't be ignored and I'm "stuck" with it.