Combining multiple column files into one with file name as first row

Hello All,

I have several column files like this

$cat a_b_s1.xls
1wert
2tg
3asd
4asdf
5asdf

$cat c_d_s2.xls
1wert
2tg
3asd
4asdf
5asdf

desired put put

$cat combined.txt
s1    s2
1wert    1wert
2tg    2tg
3asd    3asd
4asdf    4asdf
5asdf    5asdf

My current approach

ls -1 *.xls | sort > all_xls
cat all_xls | awk -F"[_.]" '{print $3}' | tr "\n" "\t" > colhead.txt
cat all_xls | tr "\n" "\t" | xargs paste > all_combined.txt
cat colhead.txt all_combined.txt > new_file.txt

Is there a better way to do this. I have formating issues with I import the new_file.txt to excel. I think its because of replacing the new line character.

Thanks

paste.

printf "s1\ts2\n" > newfile
paste file1 file2 >> newfile

Thanks, but I have more than a 100 files with very different names.