I journeyed the "which pre amp" jungle for a few years. I tried, bought and sold a few. I liked a lot of them, but not really satisfied. Finally, I found what I was looking for in a Neve 511.
I also own and really like the ISA One. The ISA One's sound and versatility to use as a 2 channel input when you use both the instrument di with the mic pre simultaneously is a big plus. More options than most pre's especially at their current pricing.
Front End Audio has a "Rack Attack" deal that's interesting. You get a discount on a 2-slot Bento Power Rack when you purchase a 500-series module from them. The deal works out to looks like this example: 511 Neve ($545) + Bento Rack ($139) = $684 (If only buying one 500 module, you may also want to also pick up a blank 500 cover panel for the empty slot for a few dollars).
http://www.frontendaudio.com/500-Series-Rack-Attack-Bundle-1-Space-p/fea0075.htm With this package, you would end up with an extra slot for adding whatever the need might be (compressor, eq, pre amp...) The Bento Rack allows you to push a button on the back to automatically rout the modules together for eq or compressor modules.