Since your choice of getting a Mastersound amp is done, this shows that you have gone beyond the no-return point as far as at LEAST trying tubes. Here is what I would do.
1. Not go through with the Mastersound, but get a different type of integrated, like maybe a small Cayin T-30, the one imported by Buzzy Bee, if you can find one. Why? First of all, it runs on relatively cheap tubes, like the EL34. You can also change tubes (tube roll) to a number of variants of the 6550 and KT 88 family. When going tubes for the first time, it is a lot of fun to experiment with different-sounding power tubes. The Cayin (and other similar integrateds) will not set you back more than $ 600 - $ 750, and replacement tubes will cost you a fraction of the 300B that the Mastersound uses. Above all, you will have tried a reliable machine, easy to bias, and will probably be able to find out if tubes are for you without emptying your bank account.
Another possible route:
I have gone from insanely expensive solid state and tube separates and integrateds (along with kilo-buck speakers, such as the Verity audio Parsifal), to a severe downgrade where I am now satisfied after years of the audiophile circus.
I a currently using (don't laugh now!) a Shanling MC-30 cd player-receiver complete with a single-ended amp built in, producing a WHOPPING 2 watts per channel! This amp is driving a pair of Opera quinta speakers, large, rich-sounding, and a perfect mate to this small wonder of an amp. Low level to moderate level volume only, but it is extraordinary in sound and resolution, smoking a past Sonic Frontiers Line 2 Power 2 combo in harmonic richness.
Why don't you give this little wonder a try? All of 600-700 will get you a tube preamp, set power amp, tuner, and a cd player that will compete with any $ 1,500.00 stand alone player when you finally add a separate power amp to it?
Read up on the MC-30 and be amazed.
Just an idea, good luck!
