I will not be able to facilitate your decision much. I used a Linn Unidisc 1.1 as both a player and transport for 12 years until the laser died and Linn, in all their wisdom, designed a proprietary laser that they no longer manufacture. AG members on the pre owned market for Unidisc models be aware. That said, without the benefit of experience or audition, reviews indicate best choices of currently marked products include Simaudio Moon, PS Audio, and Ayon.
My response, with respect, is to @clearthinker. While I fundamentally agree bits are bits and the greatest benefit-cost ratio realized with DAC improvements, improvements in a digital source, make a difference due to design differences that reduce ground, radiated, and power supply noise … and timing. A computer is not optimized in this regard to the degree of an audiophile transport or server. In my journey, I realized audible improvements with upgrades from a dedicated MacBook on battery power running I-Tunes , to the Mac running Audirvāna, to an Aurender. The progressive reduction in digital noise reduced background noise audible as a hash between images with an associated blacker background and increased detail, reduced high frequency “digital” glare, and a more organic sound. As I have said, to each our own ear-brain connection.
So Paul, from my perspective, transport improvements will be audible. Look to the recommendations you received from all. Most important, trust your own ear-brain connection. Verify if you purchase used that the manufacturer will support the product. See if they have projected a model support sunset since the industry is moving to serves. Remember my Linn experience.