Hmm. Why not send a PM?
Anyway sorry for the late reply as my internet connection was down and I could not get online.
As fellow UU brother pbagley has said, you main issue is going to be impedance mismatch, and that is going to manifest primarily as the output of your guitar or uke preamp likely not having enough gain for the input of the T-AMP, or anything else that expects a 'line-level' input.
He has some good suggestions, and if what you want is a mini-PA or practice amp kind of setup, and also be able to plug in other devices, you can usually find a cheap 4-channel mixer that will be more versatile than using a dedicated preamp such as an ART MP Studio ($59) or Behringer MIC-200 ($39), both of which will correct the impedance issue, while giving you around 80db of clean gain to play with to adjust a proper input level for the T-AMP, but the disadvantage is that you will have to unplug/replug each time, in order to use the T-AMP with other devices, unless you get an A/B/C-type of input switchbox ($25) that lets you plug everything together and then just push a button to select the source to feed the T-AMP.
Having said all that, for bookshelf speakers, I'd be cautious about running an instrument directly into them without a compressor or limiter inline before the amp, because of the percussive nature of fretted instruments you will likely damage the tweeter and woofer components if they 'bottom out' too often in their excursion (also called X-max in tech specs) when moving to produce the sound.
Instrument amplifiers are made with speaker elements inside that are designed to handle extreme excursion much more so than home stereo speakers.
Also, keep in mind that most home stereo speakers are designed to handle 'program music', meaning mixed and mastered with a somewhat consistent relative maximum volume level (also often called 'normalized'), whereas playing an instrument like guitar, bass or uke is typically anything
but a consistent maximum volume.
So one thing to consider is if you just want a cheap amp, to just get a cheap amp and not worry about all the above. I've seen them range from $50 (used) to like $150 (new) for a little 15-watt Fender Princeton or Peavey, Line6, Vox and others.
Also, Miguel, in one of your videos I saw you playing your guitar into a large amplifier, sitting on the ground (I think it was at the entrance of a Winery or art gallery) - if that guitar amplifier has a headphone jack, you can probably run that into the T-AMP input, just start with the amp's headphone volume VERY low at first so you dont blow the input circuit of the T-AMP, and you can use the controls on your amplifier to even out the sound so as to mitigate damage to the bookshelf speakers hooked up to the T-AMP as mentioned above.
Hope this helps. Please let me know how you make out.