I have a Tortuga LDR, actually two. It performs far above its price point and has trounced every preamp/controller comparison (and that includes some well known "high end" preamps).
I'd suggest an arrangement where the power amp manufacturer and Tortuga can work out a non-exclusive discount on the price of the Tortuga in exchange for including the Tortuga in a combined poweramp/preamp package.
One point. If the poweramp accepts balanced input, you'd be crazy not to include a combo package with the Tortuga LDRxB that includes absolute phase/polarity switching capability. Once you hear how important that capability is, you'll never own a system without it. The Tortuga handles that by a single click from the remote control. The Tortuga is so clean and revealing that it makes the difference between correct and incorrect absolute phase very obvious.
Best,
Robert