What is the best preamp to get for Marantz tt42

Hi Samuelsbay

This isn't the forum to get the best advice on what you are looking for. Also, best and what you can afford are not necessarily one and the same. However, we are here to help. I don't have this model but you might consider the Yamaha WXC-50. See it at Crutchfield:

https://www.crutchfield.com/p_022WXC50DS/Yamaha-WXC-50.html.

You'll still require a Sonos Connect to play your vinyl to your Play 5 an other speakers.

Cheers!

You'll still require a Sonos Connect to play your vinyl to your Play 5 an other speakers.

No, the play 5 has line in jacks that can take the wired inputs from the pre amp, so the Connect is not needed if this wiring can be conveniently done.
As to the pre amp, these are largely commodities these days, and what is more important is to get one that meets the needs of the kind of cartridge the Marantz has. A MC cartridge would need a more sensitive preamp than an MM cartridge would, unless one gets the more expensive type that can take both kinds.
Of course, an audiophile would probably disagree and want to spend a lot more in the elusive search for "the best".

Thank you for your suggestions. I shall dig a little deeper into the cartridge set up but not really wanting to go on an audiophile quest. Really just want something that will do the job well enough. I may post on other forums but thought I would try here first.