I agree with the posters who suggested you get a cheap place-holder until you can get something that will do justice to your fine amp and speakers. The preamp is, IMHO, second only to the speakers in determining the sound quality of your system. One thing I get from your posts is that you seem to be equating tubes with warmer, better sound. That is not always true, which is why an audition - in your home, with your system - is so crucial. I would look for a good used Rotel pre, with tone controls. While the Rotel probably will not bring out all your amp and speakers have to offer, it is more or less neutral in tonal balance, so you can see what a solid state pre does to the tonal balance in your system. If you find yourself adjusting the tone controls in order to enjoy the music more, you need to either eventually find a preamp that compliments your system's tonal balance better, or select a better preamp that also has tone controls or EQ (McIntosh, Classe, others).
I have been very happy with my McIntosh C220 tube-hybrid pre for the last 5 years. It offers complimentary tonal balance to my system, and does everything else pretty well, with great flexibility and features. Horses for courses, as they say.
As for Monoprice, this is a good source for non-critical cables, like ethernet cables, but other budget sources for cables might offer better performance, such as Blue Jeans Cables. I am not looking to start a flame war here, but cables should be compared in your home with your system. Go with the cheapest cable that does not seem to harm sound quality. For this you need a decent amount of time for a home trial. I personally don't belileve in spending a fortune on cables, but something above the very basic stuff Monoprice sells will probably offer better performance that you will hear. Like with the preamp, if you want to go up-market on the cables, get some place-holders from Monoprice or Blue Jeans to tide you over. These will also provide a good way to compare pricier cables when your budget permits an upgrade.
It took me many years of very selective and carefully considered upgrades (many items bought used) to reach the point where upgrades are something I would only do if I suddenly had a lot more disposable income than I do currently. I have a very budget-friendly system that I enjoy listening to for long listening sessions whenever I get the chance. When I listen, I simply enjoy, with no nagging feeling that this or that aspect of the sound could be better to ruin my pleasure. I've heard many pricier systems that I would not trade my own for. But that is the result of luck, careful, well-researched (and opportunistic) purchases, and critical auditioning.